Deck Post Spacing Chart: How Far Apart Should Deck Posts Be?
Quick answer: Deck posts are often spaced around 6 to 8 feet apart in common residential layouts, but there is no universal maximum spacing. Structural deck post spacing is determined by the allowable span of the beam between posts.
A larger beam may allow posts to be farther apart, while longer joists, heavier loads, cantilevers, or weaker lumber may require posts to be closer together.
The key rule: Determine the allowable beam span first, then lay out the posts so no beam span exceeds that limit.
Post spacing is the support-layout result of the beam design. Start with the Deck Beam Span Chart, then use this guide to turn the allowable beam span into actual post locations and post count.
Deck Post Spacing Chart
The table below shows how the allowable distance between deck posts can change with beam size and joist span.
These are Southern Pine, No. 2, wet-service planning examples from the IRC 40 psf live-load / 10 psf dead-load beam table for the no-joist-cantilever conditions shown here. Current IRC tables also account for effective joist span when a joist cantilever is present. Your locally adopted code, lumber species, grade, design load, cantilever, and other framing conditions may produce different allowable spans.
| Beam Size | 6-ft Joist Span | 8-ft Joist Span | 10-ft Joist Span | 12-ft Joist Span | 14-ft Joist Span | 16-ft Joist Span |
|---|---|---|---|---|---|---|
| Double 2×6 | 6′-11″ | 5′-11″ | 5′-4″ | 4′-10″ | 4′-6″ | 4′-3″ |
| Double 2×8 | 8′-9″ | 7′-7″ | 6′-9″ | 6′-2″ | 5′-9″ | 5′-4″ |
| Double 2×10 | 10′-4″ | 9′-0″ | 8′-0″ | 7′-4″ | 6′-9″ | 6′-4″ |
| Double 2×12 | 12′-2″ | 10′-7″ | 9′-5″ | 8′-7″ | 8′-0″ | 7′-6″ |
| Triple 2×10 | 13′-0″ | 11′-3″ | 10′-0″ | 9′-2″ | 8′-6″ | 7′-11″ |
| Triple 2×12 | 15′-3″ | 13′-3″ | 11′-10″ | 10′-9″ | 10′-0″ | 9′-4″ |
Important: Do not treat this as a universal post-spacing table. These are Southern Pine, No. 2, wet-service planning values for the 40 psf live-load / 10 psf dead-load condition shown. The chart uses the no-joist-cantilever condition. Current IRC beam tables use additional effective-joist-span conditions when cantilever is present. Snow load, species, grade, local amendments, and other conditions can change the permitted beam span.
For complete beam-sizing guidance, see our Deck Beam Span Chart .
How to Read the Deck Post Spacing Chart
Start with the length of the joists that load the beam, then find the beam size you plan to use.
The value where that row and column intersect represents the example allowable beam span between supports under the stated conditions.
Maximum post spacing ≈ allowable beam span between supports.
For example, a double 2×10 supporting approximately 12-foot joists is shown with an example maximum span of 7 feet 4 inches. That does not mean the posts can automatically be moved to 8 feet apart simply because 8 feet is a convenient layout dimension.
A larger beam under the same joist-span condition may allow substantially wider spacing.
See How Beam Size Changes Post Spacing
The deck does not change in the two examples below. The joists still span 12 feet and the exterior beam still runs 16 feet. Only the beam size changes.
Watch the support layout: a beam with a longer allowable span can use fewer posts because each beam span is permitted to be longer.
Beam size → allowable beam span → post spacing → post count → footing reactions.
A larger beam can reduce the number of supports, but each remaining post and footing may carry more load. Fewer posts are not automatically the better design.
Planning example only. Actual design must use the applicable code edition, lumber species and grade, loads, joist cantilever condition, beam cantilever, post capacity, footing capacity, connection details, and local amendments.
Example: Deck Post Spacing for a 12×16 Deck
Consider a 12-foot-deep by 16-foot-wide attached deck.
Assume:
- joists run approximately 12 feet from the house toward the exterior beam
- the beam runs along the 16-foot width
- there is one exterior beam line
- there is no significant joist cantilever for this simplified example
Now compare several Southern Pine beam options using the applicable 12-foot joist-span condition:
| Beam | Example Maximum Span | What It Means for a 16-ft Beam |
|---|---|---|
| Double 2×8 | 6′-2″ | At least 3 beam spans / 4 posts |
| Double 2×10 | 7′-4″ | At least 3 beam spans / 4 posts |
| Double 2×12 | 8′-7″ | 2 spans / 3 posts can fit |
| Triple 2×10 | 9′-2″ | 2 spans / 3 posts can fit |
| Triple 2×12 | 10′-9″ | 2 spans / 3 posts can fit |
This is why deck dimensions alone cannot determine how many posts you need. Changing the beam changes the possible post layout.
Structural Deck Posts vs. Railing Posts
This guide covers structural support posts beneath deck beams.
It does not cover guard or railing post spacing.
Structural Support Posts
- support deck beams
- carry vertical gravity loads
- transfer beam reactions into footings
- affect beam span and footing loads
Railing Posts
- support the deck guard
- resist lateral loads
- follow separate structural requirements
- depend on the railing system and connections
If you are looking for guard-post requirements, see our Deck Railing Post Spacing Guide .
What Determines Deck Post Spacing?
| Structural Factor | Effect on Post Layout |
|---|---|
| Beam size | Larger or stronger beams can generally span farther between supports. |
| Number of beam plies | Adding an approved beam ply can increase allowable span. |
| Joist span | Longer joists generally increase the load delivered to the beam. |
| Joist cantilever | Overhanging joists add load beyond the beam and can reduce allowable beam span. |
| Lumber species & grade | Different wood properties produce different allowable spans. |
| Design load | Higher required loads generally reduce allowable spans. |
| Footing capacity | Wider post spacing can increase the reaction each footing must carry. |
| Soil bearing capacity | Lower allowable soil pressure can require larger footing area. |
| Post height & size | The post itself must be adequate for its tributary load and unsupported height. |
Why Beam and Joist Span Control Deck Post Spacing
Deck loads move through a predictable structural path:
decking → joists → beam → posts → footings → soil
The joists collect load from the deck surface and transfer it into their supports. The beam then carries that load between structural posts.
For a conventional straight beam supported by posts, the distance between adjacent posts establishes the actual beam span.
Move the posts farther apart → the beam must span farther.
Move the posts closer together → the beam spans less.
Longer joists generally increase the load delivered to the exterior beam. That increased beam load can reduce how far a particular beam is permitted to span between posts.
Shorter joists → lower beam reaction → potentially wider post spacing.
Longer joists → higher beam reaction → potentially closer post spacing.
This is why a double 2×10 does not have one universal deck-post-spacing limit.
Related: Deck Joist Span Chart and Deck Joist Spacing Guide .
What Is Tributary Area?
Tributary area is the portion of the deck surface whose load is carried by a particular structural member.
For posts, think of each post as supporting part of the beam while that section of beam supports part of the joist system above it.
An interior post usually receives load from beam spans on both sides. An end post generally receives load from only one adjacent span, plus any beam cantilever beyond the post.
Wider post spacing can increase both beam span and the tributary load carried by each post and footing.
This is why removing a post may require both a larger beam and a larger footing.
Can Deck Posts Be 6 Feet Apart?
Yes. Six-foot post spacing falls within the allowable range of many common residential beam configurations when the beam, joist span, loading, and other framing conditions support it.
Closer post spacing reduces the distance the beam has to span and may allow a smaller beam than a layout using wider post spacing.
Six feet is a practical layout option on many decks, but it is not a universal requirement.
Is 8-Foot Deck Post Spacing Standard?
Eight feet appears frequently in residential deck layouts because it is a convenient dimension and many common beam configurations can fall somewhere near that range under suitable loading conditions.
But 8 feet is not a universal code rule.
Depending on the framing system:
- a smaller beam may need posts substantially closer than 8 feet
- a larger beam may be permitted to span farther than 8 feet
- long joists may make an 8-foot span too large
- short joists may allow considerably more than 8 feet
- higher design loads may reduce allowable spacing
Do not begin a structural deck layout by assuming “posts every 8 feet.”
Determine the allowable beam span first.
Can Deck Posts Be 10 Feet Apart?
Yes. Some residential deck beam configurations can support approximately 10 feet between posts.
But 10-foot spacing is not automatically acceptable simply because the beam uses 2×10 or 2×12 lumber.
For example, under the Southern Pine planning table above, a double 2×10 supporting a 12-foot joist span is limited to substantially less than 10 feet, while a triple 2×12 under the same joist-span condition can exceed 10 feet.
Whether 10-foot post spacing works depends on the complete beam and loading configuration.
Can Deck Posts Be 12 Feet Apart?
Sometimes, but this is where generic deck-post-spacing advice becomes especially risky.
A sufficiently large beam carrying a relatively small tributary load may be able to span 12 feet or more. The same beam carrying much longer joists may not.
“Can posts be 12 feet apart?” is really the question: “Can this specific beam safely span 12 feet under this specific load?”
If the applicable prescriptive table does not permit the required span, the solution may be to:
- add another post
- increase beam size
- change the framing layout
- reduce the joist span
- use an engineered beam or engineered design
How to Determine Deck Post Spacing Step by Step
- Determine the deck dimensions.
- Choose the joist direction.
- Determine the applicable design load.
- Select joist size, species, and spacing.
- Determine the actual joist span.
- Account for any joist cantilever.
- Select a candidate beam size and species.
- Look up the maximum allowable beam span.
- Lay out posts so every beam span remains within that limit.
- Check any beam cantilevers.
- Calculate the load at each post.
- Size the posts and footings for those reactions.
- Verify the complete layout against your locally adopted code.
Correct sequence:
Joists → Beam → Posts → Footings
Do not choose the post spacing first and try to force the rest of the framing to fit it.
How Many Deck Posts Do You Need?
Once you know the allowable beam span, estimating post count becomes much easier.
For a simple straight beam with posts at both ends and no beam cantilever:
Number of beam spans = Round Up (Beam Length ÷ Maximum Allowable Span)
Number of posts = Number of spans + 1
Example: 16-Foot Beam
Suppose your approved beam configuration can span a maximum of 8 feet.
16 ÷ 8 = 2 spans
Two beam spans require three posts:
Post — 8 ft — Post — 8 ft — Post
Example: 20-Foot Beam
Suppose the same beam can span 8 feet.
20 ÷ 8 = 2.5
Round up to three spans.
Three beam spans require four posts.
The posts can then be distributed so none of the actual spans exceeds the allowable maximum.
Important: Beam cantilevers, unequal spans, corners, freestanding layouts, multiple beam lines, concentrated loads, and other configurations can change this simple calculation.
Continue with our How Many Deck Posts Do I Need? guide, then our How Many Footings Do I Need for a Deck? guide.
Deck Post Spacing vs. Footing Spacing
On a conventional beam-and-post deck, each structural post typically bears on its own footing.
That means the footing layout generally follows the structural post layout.
But footing spacing and footing size are different decisions.
- Post/footing spacing: where the supports are located
- Footing size: how much bearing area each support requires
- Footing depth: how deep the foundation must extend based on frost, soil, and local requirements
Wider post spacing can mean fewer footings, but each remaining footing may need to support more load.
Continue with our Deck Footing Size Chart and Deck Footing Spacing Guide .
Can You Use Fewer Deck Posts?
Often, yes, but reducing the post count changes the structural system.
Removing a post usually creates a longer beam span.
That may require:
- a deeper beam
- an additional beam ply
- a stronger lumber species
- an engineered beam
- larger post reactions
- larger footings
Fewer posts does not mean less structure.
You are concentrating the deck load into fewer support locations.
This can still be a good design choice when fewer posts improve patio clearance, appearance, access, or construction around obstacles.
More Posts vs. Larger Beam: Which Is Better?
| Strategy | Advantages | Tradeoffs |
|---|---|---|
| More posts / shorter spans | Smaller beam may work; reduced beam span | More footings, excavation, hardware, and obstructions below deck |
| Fewer posts / longer spans | Cleaner area beneath deck; fewer footings | Larger beam and potentially larger footing loads |
| Additional beam line | Shorter joist spans and potentially stiffer framing | Additional posts, beams, footings, and labor |
There is no universal best layout.
The goal is to find the most efficient combination of beam size, post count, footing size, cost, and usable space.
What Size Should Deck Posts Be?
Post size is a separate structural calculation from post spacing.
The appropriate post size depends on variables including:
- post height
- tributary area
- lumber species
- design load
- bracing and restraint
- applicable prescriptive limits
| Post Size | General Context |
|---|---|
| 4×4 | Can be permitted in limited prescriptive conditions depending on height and load |
| 4×6 | Permitted in some structural configurations |
| 6×6 | Very common for modern residential deck support |
| Larger / engineered | May be used for tall, heavily loaded, or engineered structures |
6×6 is common, but it is not a universal requirement for every residential deck.
Do not select a post size solely because it is commonly used.
Beam-to-Post Connections Matter
A correctly spaced post still needs a proper load path from the beam into the post.
For conventional prescriptive wood framing, the beam needs actual bearing at the support rather than simply hanging from the side of the post on through-bolts.
Common approaches include:
- beam bearing on top of the post with an approved post cap or connector
- beam bearing in a properly detailed post notch where permitted
- another approved structural connection providing the required bearing and restraint
Do not assume that bolting a beam to the side of a post creates an acceptable gravity-load connection.
The beam also needs appropriate restraint against lateral displacement at its supports.
See the Deck Post-to-Beam Connection Guide for bearing, notched-post, post-cap, and side-bolted connection details.
Post-to-Footing Connections Matter Too
The load path continues below the post.
A post-base connection can help locate and secure the post while keeping the wood appropriately separated from concrete where required by the selected connector and construction detail.
The connector must be appropriate for:
- the post size
- the foundation type
- the required loads
- the treated-lumber environment
- the specified fasteners and anchors
A post base does not make an undersized footing adequate.
The connector and footing perform different structural jobs.
How Beam Cantilever Changes Post Layout
The outside posts do not always have to sit directly beneath the ends of the beam.
A beam can cantilever beyond its outside bearing locations when the framing satisfies the applicable requirements.
Current IRC prescriptive deck provisions limit a beam cantilever beyond a bearing location to one-fourth of the actual adjacent beam span for the applicable prescriptive beam configuration.
Example
If the actual outer beam span between posts is 8 feet:
8 ft ÷ 4 = 2-ft maximum beam cantilever
Beam cantilever can move the outside posts inward, but it does not increase the allowable span between the posts.
See our Deck Cantilever Guide for joist and beam cantilever guidance.
How Joist Cantilever Affects Post Spacing
Joist cantilever and beam cantilever are different.
When joists extend beyond a drop beam, the cantilevered deck area still contributes load to the beam.
As that joist cantilever increases, beam demand can increase.
That can reduce the allowable span between posts for a given beam configuration.
A joist cantilever can change the beam span you are allowed to use.
Current IRC beam tables address this by using effective deck joist span conditions that account for the relationship between actual joist span and cantilever. This is why cantilevered deck layouts should be checked against the specific table conditions rather than a generic post-spacing rule.
How Snow Load Changes Deck Post Spacing
Higher design loads place greater demand on the entire support system.
In higher-snow-load areas, a deck may require:
- shorter beam spans
- larger beams
- additional posts
- larger footings
- different joist sizing
Do not use a 40 psf residential span table automatically if your jurisdiction requires a higher deck design load.
Check the design criteria required by the local building department before using any prescriptive span chart.
How Soil Conditions Affect Deck Post Layout
The beam determines where structural reactions occur, but the soil ultimately has to support those reactions.
Lower allowable soil-bearing capacity generally requires more footing area for the same post load.
Therefore, increasing post spacing can create a chain reaction:
wider post spacing → longer beam spans → larger post reactions → potentially larger footings
This is why post spacing should not be optimized only around reducing the number of holes you need to dig.
Common Deck Post Spacing Mistakes
1. Assuming Every Deck Uses 8-Foot Post Spacing
Eight feet is common, not universal.
2. Choosing Post Locations Before Sizing the Beam
The allowable beam span should establish the maximum spacing.
3. Ignoring Joist Span
Longer joists can substantially increase the beam load and reduce allowable post spacing.
4. Ignoring Joist Cantilever
Cantilevered deck area still contributes load to the supporting beam.
5. Using a Beam Table for the Wrong Species
Identically sized beams can have different allowable spans depending on species and grade.
6. Removing a Post Without Checking the Footings
Fewer posts can increase the load carried by each remaining footing.
7. Confusing Structural Posts With Railing Posts
They perform completely different structural jobs and follow different design requirements.
8. Side-Bolting a Beam Without Proper Bearing
A beam needs an approved load path into the post.
9. Designing Every Member at Its Absolute Maximum
Code span limits establish structural boundaries; shorter spans can also improve stiffness and simplify construction.
Signs an Existing Deck Support System Needs Attention
Possible warning signs include:
- visible beam sagging between posts
- leaning or twisted posts
- posts no longer centered on footings
- movement at beam-to-post connections
- settled or heaved footings
- significant deck bounce
- cracked, deteriorated, or damaged posts
- beam splices without proper bearing
- corroded or loose connectors
Adding another post is not automatically the correct repair.
Movement can originate from the beam, footing, ledger, joists, connections, soil, or several components working together.
Use our Deck Inspection Checklist when evaluating an existing structure.
How Post Spacing Affects Deck Cost
Post spacing creates a structural and economic tradeoff.
| Layout Choice | Potential Savings | Potential Added Cost |
|---|---|---|
| Closer posts | Smaller beam may work | More posts, footings, excavation, connectors |
| Wider posts | Fewer foundations | Larger beam and potentially larger footings |
| Engineered long span | Open area below deck | Higher beam and engineering cost |
For some decks, adding one inexpensive support post is cheaper than increasing the beam size across the entire deck.
For others, fewer posts are worth the additional beam cost because they preserve usable space below the deck.
Related: Deck Framing Cost Guide .
Recommended Tools & Hardware for Deck Post Layout
Once the structural post locations are established on paper, the next job is transferring that layout accurately to the site.
For most DIY deck builders, we would prioritize accurate measuring and layout tools first. Structural connectors come later and should be selected only after the exact beam, post, and footing details are known.
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Bosch BLAZE Pro GLM165-40 Laser Measure
Our first upgrade for laying out a larger deck: the Bosch GLM165-40 makes it much easier to repeatedly check beam runs, overall dimensions, post locations, and longer layout distances without fighting a tape measure across the entire site.
Best for: Beam runs, deck dimensions, post spacing, footing layout, and repeated long-distance measurements.
Buy if: You are laying out a full deck and expect to make repeated measurements longer than a conventional tape is convenient for.
Skip if: You already own a dependable laser measure or are working on a small layout where a quality tape handles everything comfortably.
Layout note: A laser measure improves measurement efficiency, but it does not establish the structural post locations for you. Determine the allowable beam spans first, then transfer those approved dimensions to the site.
Three Tools for Transferring the Post Layout
The laser handles longer measurements. A tape, square, and good marking tool handle the close-range work around beams, posts, batter boards, framing, and hardware.
Stanley FATMAX 25-Foot Tape Measure
A dependable tape remains faster than a laser for short measurements, offsets, post dimensions, hardware placement, and everyday framing checks.
Best for: Short layout measurements and general deck framing.
Swanson 7-Inch Speed Square
One of the highest-value tools in a deck-building kit for square marks, framing layout, checking cuts, and transferring dimensions around posts and beams.
Best for: Framing marks, square references, and everyday layout work.
Deck Post Spacing Chart: How Far Apart Should Deck Posts Be?
Quick answer: Deck posts are often spaced around 6 to 8 feet apart in common residential layouts, but there is no universal maximum spacing. Structural deck post spacing is determined by the allowable span of the beam between posts.
A larger beam may allow posts to be farther apart, while longer joists, heavier loads, cantilevers, or weaker lumber may require posts to be closer together.
The key rule: Determine the allowable beam span first, then lay out the posts so no beam span exceeds that limit.
Post spacing is the support-layout result of the beam design. Start with the Deck Beam Span Chart, then use this guide to turn the allowable beam span into actual post locations and post count.
Deck Post Spacing Chart
The table below shows how the allowable distance between deck posts can change with beam size and joist span.
These are Southern Pine, No. 2, wet-service planning examples from the IRC 40 psf live-load / 10 psf dead-load beam table for the no-joist-cantilever conditions shown here. Current IRC tables also account for effective joist span when a joist cantilever is present. Your locally adopted code, lumber species, grade, design load, cantilever, and other framing conditions may produce different allowable spans.
| Beam Size | 6-ft Joist Span | 8-ft Joist Span | 10-ft Joist Span | 12-ft Joist Span | 14-ft Joist Span | 16-ft Joist Span |
|---|---|---|---|---|---|---|
| Double 2×6 | 6′-11″ | 5′-11″ | 5′-4″ | 4′-10″ | 4′-6″ | 4′-3″ |
| Double 2×8 | 8′-9″ | 7′-7″ | 6′-9″ | 6′-2″ | 5′-9″ | 5′-4″ |
| Double 2×10 | 10′-4″ | 9′-0″ | 8′-0″ | 7′-4″ | 6′-9″ | 6′-4″ |
| Double 2×12 | 12′-2″ | 10′-7″ | 9′-5″ | 8′-7″ | 8′-0″ | 7′-6″ |
| Triple 2×10 | 13′-0″ | 11′-3″ | 10′-0″ | 9′-2″ | 8′-6″ | 7′-11″ |
| Triple 2×12 | 15′-3″ | 13′-3″ | 11′-10″ | 10′-9″ | 10′-0″ | 9′-4″ |
Important: Do not treat this as a universal post-spacing table. These are Southern Pine, No. 2, wet-service planning values for the 40 psf live-load / 10 psf dead-load condition shown. The chart uses the no-joist-cantilever condition. Current IRC beam tables use additional effective-joist-span conditions when cantilever is present. Snow load, species, grade, local amendments, and other conditions can change the permitted beam span.
For complete beam-sizing guidance, see our Deck Beam Span Chart .
How to Read the Deck Post Spacing Chart
Start with the length of the joists that load the beam, then find the beam size you plan to use.
The value where that row and column intersect represents the example allowable beam span between supports under the stated conditions.
Maximum post spacing ≈ allowable beam span between supports.
For example, a double 2×10 supporting approximately 12-foot joists is shown with an example maximum span of 7 feet 4 inches. That does not mean the posts can automatically be moved to 8 feet apart simply because 8 feet is a convenient layout dimension.
A larger beam under the same joist-span condition may allow substantially wider spacing.
See Why Beam Size Changes Deck Post Spacing
Both examples use the same simplified 12×16 attached deck with a 12-foot joist span, a 16-foot exterior beam run, and no joist or beam cantilever. Only the beam size changes.
Double 2×10
Example allowable beam span: 7 ft 4 in.
Double 2×12
Example allowable beam span: 8 ft 7 in.
Same deck. Different beam. Different support layout.
Beam size → allowable beam span → post spacing → post count.
Planning illustration, not a construction drawing. The example values use the Southern Pine assumptions stated in the chart above.
Example: Deck Post Spacing for a 12×16 Deck
Consider a 12-foot-deep by 16-foot-wide attached deck.
Assume:
- joists run approximately 12 feet from the house toward the exterior beam
- the beam runs along the 16-foot width
- there is one exterior beam line
- there is no significant joist cantilever for this simplified example
Now compare several Southern Pine beam options using the applicable 12-foot joist-span condition:
| Beam | Example Maximum Span | What It Means for a 16-ft Beam |
|---|---|---|
| Double 2×8 | 6′-2″ | At least 3 beam spans / 4 posts |
| Double 2×10 | 7′-4″ | At least 3 beam spans / 4 posts |
| Double 2×12 | 8′-7″ | 2 spans / 3 posts can fit |
| Triple 2×10 | 9′-2″ | 2 spans / 3 posts can fit |
| Triple 2×12 | 10′-9″ | 2 spans / 3 posts can fit |
This is why deck dimensions alone cannot determine how many posts you need. Changing the beam changes the possible post layout.
Structural Deck Posts vs. Railing Posts
This guide covers structural support posts beneath deck beams.
It does not cover guard or railing post spacing.
Structural Support Posts
- support deck beams
- carry vertical gravity loads
- transfer beam reactions into footings
- affect beam span and footing loads
Railing Posts
- support the deck guard
- resist lateral loads
- follow separate structural requirements
- depend on the railing system and connections
If you are looking for guard-post requirements, see our Deck Railing Post Spacing Guide .
What Determines Deck Post Spacing?
| Structural Factor | Effect on Post Layout |
|---|---|
| Beam size | Larger or stronger beams can generally span farther between supports. |
| Number of beam plies | Adding an approved beam ply can increase allowable span. |
| Joist span | Longer joists generally increase the load delivered to the beam. |
| Joist cantilever | Overhanging joists add load beyond the beam and can reduce allowable beam span. |
| Lumber species & grade | Different wood properties produce different allowable spans. |
| Design load | Higher required loads generally reduce allowable spans. |
| Footing capacity | Wider post spacing can increase the reaction each footing must carry. |
| Soil bearing capacity | Lower allowable soil pressure can require larger footing area. |
| Post height & size | The post itself must be adequate for its tributary load and unsupported height. |
Why Beam and Joist Span Control Deck Post Spacing
Deck loads move through a predictable structural path:
decking → joists → beam → posts → footings → soil
The joists collect load from the deck surface and transfer it into their supports. The beam then carries that load between structural posts.
For a conventional straight beam supported by posts, the distance between adjacent posts establishes the actual beam span.
Move the posts farther apart → the beam must span farther.
Move the posts closer together → the beam spans less.
Longer joists generally increase the load delivered to the exterior beam. That increased beam load can reduce how far a particular beam is permitted to span between posts.
Shorter joists → lower beam reaction → potentially wider post spacing.
Longer joists → higher beam reaction → potentially closer post spacing.
This is why a double 2×10 does not have one universal deck-post-spacing limit.
Related: Deck Joist Span Chart and Deck Joist Spacing Guide .
What Is Tributary Area?
Tributary area is the portion of the deck surface whose load is carried by a particular structural member.
For posts, think of each post as supporting part of the beam while that section of beam supports part of the joist system above it.
An interior post usually receives load from beam spans on both sides. An end post generally receives load from only one adjacent span, plus any beam cantilever beyond the post.
Wider post spacing can increase both beam span and the tributary load carried by each post and footing.
This is why removing a post may require both a larger beam and a larger footing.
Can Deck Posts Be 6 Feet Apart?
Yes. Six-foot post spacing falls within the allowable range of many common residential beam configurations when the beam, joist span, loading, and other framing conditions support it.
Closer post spacing reduces the distance the beam has to span and may allow a smaller beam than a layout using wider post spacing.
Six feet is a practical layout option on many decks, but it is not a universal requirement.
Is 8-Foot Deck Post Spacing Standard?
Eight feet appears frequently in residential deck layouts because it is a convenient dimension and many common beam configurations can fall somewhere near that range under suitable loading conditions.
But 8 feet is not a universal code rule.
Depending on the framing system:
- a smaller beam may need posts substantially closer than 8 feet
- a larger beam may be permitted to span farther than 8 feet
- long joists may make an 8-foot span too large
- short joists may allow considerably more than 8 feet
- higher design loads may reduce allowable spacing
Do not begin a structural deck layout by assuming “posts every 8 feet.”
Determine the allowable beam span first.
Can Deck Posts Be 10 Feet Apart?
Yes. Some residential deck beam configurations can support approximately 10 feet between posts.
But 10-foot spacing is not automatically acceptable simply because the beam uses 2×10 or 2×12 lumber.
For example, under the Southern Pine planning table above, a double 2×10 supporting a 12-foot joist span is limited to substantially less than 10 feet, while a triple 2×12 under the same joist-span condition can exceed 10 feet.
Whether 10-foot post spacing works depends on the complete beam and loading configuration.
Can Deck Posts Be 12 Feet Apart?
Sometimes, but this is where generic deck-post-spacing advice becomes especially risky.
A sufficiently large beam carrying a relatively small tributary load may be able to span 12 feet or more. The same beam carrying much longer joists may not.
“Can posts be 12 feet apart?” is really the question: “Can this specific beam safely span 12 feet under this specific load?”
If the applicable prescriptive table does not permit the required span, the solution may be to:
- add another post
- increase beam size
- change the framing layout
- reduce the joist span
- use an engineered beam or engineered design
How to Determine Deck Post Spacing Step by Step
- Determine the deck dimensions.
- Choose the joist direction.
- Determine the applicable design load.
- Select joist size, species, and spacing.
- Determine the actual joist span.
- Account for any joist cantilever.
- Select a candidate beam size and species.
- Look up the maximum allowable beam span.
- Lay out posts so every beam span remains within that limit.
- Check any beam cantilevers.
- Calculate the load at each post.
- Size the posts and footings for those reactions.
- Verify the complete layout against your locally adopted code.
Correct sequence:
Joists → Beam → Posts → Footings
Do not choose the post spacing first and try to force the rest of the framing to fit it.
How Many Deck Posts Do You Need?
Once you know the allowable beam span, estimating post count becomes much easier.
For a simple straight beam with posts at both ends and no beam cantilever:
Number of beam spans = Round Up (Beam Length ÷ Maximum Allowable Span)
Number of posts = Number of spans + 1
Example: 16-Foot Beam
Suppose your approved beam configuration can span a maximum of 8 feet.
16 ÷ 8 = 2 spans
Two beam spans require three posts:
Post — 8 ft — Post — 8 ft — Post
Example: 20-Foot Beam
Suppose the same beam can span 8 feet.
20 ÷ 8 = 2.5
Round up to three spans.
Three beam spans require four posts.
The posts can then be distributed so none of the actual spans exceeds the allowable maximum.
Important: Beam cantilevers, unequal spans, corners, freestanding layouts, multiple beam lines, concentrated loads, and other configurations can change this simple calculation.
Continue with our How Many Deck Posts Do I Need? guide, then our How Many Footings Do I Need for a Deck? guide.
Deck Post Spacing vs. Footing Spacing
On a conventional beam-and-post deck, each structural post typically bears on its own footing.
That means the footing layout generally follows the structural post layout.
But footing spacing and footing size are different decisions.
- Post/footing spacing: where the supports are located
- Footing size: how much bearing area each support requires
- Footing depth: how deep the foundation must extend based on frost, soil, and local requirements
Wider post spacing can mean fewer footings, but each remaining footing may need to support more load.
Continue with our Deck Footing Size Chart and Deck Footing Spacing Guide .
Can You Use Fewer Deck Posts?
Often, yes, but reducing the post count changes the structural system.
Removing a post usually creates a longer beam span.
That may require:
- a deeper beam
- an additional beam ply
- a stronger lumber species
- an engineered beam
- larger post reactions
- larger footings
Fewer posts does not mean less structure.
You are concentrating the deck load into fewer support locations.
This can still be a good design choice when fewer posts improve patio clearance, appearance, access, or construction around obstacles.
More Posts vs. Larger Beam: Which Is Better?
| Strategy | Advantages | Tradeoffs |
|---|---|---|
| More posts / shorter spans | Smaller beam may work; reduced beam span | More footings, excavation, hardware, and obstructions below deck |
| Fewer posts / longer spans | Cleaner area beneath deck; fewer footings | Larger beam and potentially larger footing loads |
| Additional beam line | Shorter joist spans and potentially stiffer framing | Additional posts, beams, footings, and labor |
There is no universal best layout.
The goal is to find the most efficient combination of beam size, post count, footing size, cost, and usable space.
What Size Should Deck Posts Be?
Post size is a separate structural calculation from post spacing.
The appropriate post size depends on variables including:
- post height
- tributary area
- lumber species
- design load
- bracing and restraint
- applicable prescriptive limits
| Post Size | General Context |
|---|---|
| 4×4 | Can be permitted in limited prescriptive conditions depending on height and load |
| 4×6 | Permitted in some structural configurations |
| 6×6 | Very common for modern residential deck support |
| Larger / engineered | May be used for tall, heavily loaded, or engineered structures |
6×6 is common, but it is not a universal requirement for every residential deck.
Do not select a post size solely because it is commonly used.
Beam-to-Post Connections Matter
A correctly spaced post still needs a proper load path from the beam into the post.
For conventional prescriptive wood framing, the beam needs actual bearing at the support rather than simply hanging from the side of the post on through-bolts.
Common approaches include:
- beam bearing on top of the post with an approved post cap or connector
- beam bearing in a properly detailed post notch where permitted
- another approved structural connection providing the required bearing and restraint
Do not assume that bolting a beam to the side of a post creates an acceptable gravity-load connection.
The beam also needs appropriate restraint against lateral displacement at its supports.
See the Deck Post-to-Beam Connection Guide for bearing, notched-post, post-cap, and side-bolted connection details.
Post-to-Footing Connections Matter Too
The load path continues below the post.
A post-base connection can help locate and secure the post while keeping the wood appropriately separated from concrete where required by the selected connector and construction detail.
The connector must be appropriate for:
- the post size
- the foundation type
- the required loads
- the treated-lumber environment
- the specified fasteners and anchors
A post base does not make an undersized footing adequate.
The connector and footing perform different structural jobs.
How Beam Cantilever Changes Post Layout
The outside posts do not always have to sit directly beneath the ends of the beam.
A beam can cantilever beyond its outside bearing locations when the framing satisfies the applicable requirements.
Current IRC prescriptive deck provisions limit a beam cantilever beyond a bearing location to one-fourth of the actual adjacent beam span for the applicable prescriptive beam configuration.
Example
If the actual outer beam span between posts is 8 feet:
8 ft ÷ 4 = 2-ft maximum beam cantilever
Beam cantilever can move the outside posts inward, but it does not increase the allowable span between the posts.
See our Deck Cantilever Guide for joist and beam cantilever guidance.
How Joist Cantilever Affects Post Spacing
Joist cantilever and beam cantilever are different.
When joists extend beyond a drop beam, the cantilevered deck area still contributes load to the beam.
As that joist cantilever increases, beam demand can increase.
That can reduce the allowable span between posts for a given beam configuration.
A joist cantilever can change the beam span you are allowed to use.
Current IRC beam tables address this by using effective deck joist span conditions that account for the relationship between actual joist span and cantilever. This is why cantilevered deck layouts should be checked against the specific table conditions rather than a generic post-spacing rule.
How Snow Load Changes Deck Post Spacing
Higher design loads place greater demand on the entire support system.
In higher-snow-load areas, a deck may require:
- shorter beam spans
- larger beams
- additional posts
- larger footings
- different joist sizing
Do not use a 40 psf residential span table automatically if your jurisdiction requires a higher deck design load.
Check the design criteria required by the local building department before using any prescriptive span chart.
How Soil Conditions Affect Deck Post Layout
The beam determines where structural reactions occur, but the soil ultimately has to support those reactions.
Lower allowable soil-bearing capacity generally requires more footing area for the same post load.
Therefore, increasing post spacing can create a chain reaction:
wider post spacing → longer beam spans → larger post reactions → potentially larger footings
This is why post spacing should not be optimized only around reducing the number of holes you need to dig.
Common Deck Post Spacing Mistakes
1. Assuming Every Deck Uses 8-Foot Post Spacing
Eight feet is common, not universal.
2. Choosing Post Locations Before Sizing the Beam
The allowable beam span should establish the maximum spacing.
3. Ignoring Joist Span
Longer joists can substantially increase the beam load and reduce allowable post spacing.
4. Ignoring Joist Cantilever
Cantilevered deck area still contributes load to the supporting beam.
5. Using a Beam Table for the Wrong Species
Identically sized beams can have different allowable spans depending on species and grade.
6. Removing a Post Without Checking the Footings
Fewer posts can increase the load carried by each remaining footing.
7. Confusing Structural Posts With Railing Posts
They perform completely different structural jobs and follow different design requirements.
8. Side-Bolting a Beam Without Proper Bearing
A beam needs an approved load path into the post.
9. Designing Every Member at Its Absolute Maximum
Code span limits establish structural boundaries; shorter spans can also improve stiffness and simplify construction.
Signs an Existing Deck Support System Needs Attention
Possible warning signs include:
- visible beam sagging between posts
- leaning or twisted posts
- posts no longer centered on footings
- movement at beam-to-post connections
- settled or heaved footings
- significant deck bounce
- cracked, deteriorated, or damaged posts
- beam splices without proper bearing
- corroded or loose connectors
Adding another post is not automatically the correct repair.
Movement can originate from the beam, footing, ledger, joists, connections, soil, or several components working together.
Use our Deck Inspection Checklist when evaluating an existing structure.
How Post Spacing Affects Deck Cost
Post spacing creates a structural and economic tradeoff.
| Layout Choice | Potential Savings | Potential Added Cost |
|---|---|---|
| Closer posts | Smaller beam may work | More posts, footings, excavation, connectors |
| Wider posts | Fewer foundations | Larger beam and potentially larger footings |
| Engineered long span | Open area below deck | Higher beam and engineering cost |
For some decks, adding one inexpensive support post is cheaper than increasing the beam size across the entire deck.
For others, fewer posts are worth the additional beam cost because they preserve usable space below the deck.
Related: Deck Framing Cost Guide .
Recommended Tools & Hardware for Deck Post Layout
Once the structural post locations are established on paper, the next job is transferring that layout accurately to the site.
For most DIY deck builders, we would prioritize accurate measuring and layout tools first. Structural connectors come later and should be selected only after the exact beam, post, and footing details are known.
Disclosure: As an Amazon Associate, The Backyard Standard may earn from qualifying purchases at no additional cost to you. Product recommendations are selected for their relevance to the task, not simply because an affiliate link is available.
Bosch BLAZE Pro GLM165-40 Laser Measure
Our first upgrade for laying out a larger deck: the Bosch GLM165-40 makes it much easier to repeatedly check beam runs, overall dimensions, post locations, and longer layout distances without fighting a tape measure across the entire site.
Best for: Beam runs, deck dimensions, post spacing, footing layout, and repeated long-distance measurements.
Buy if: You are laying out a full deck and expect to make repeated measurements longer than a conventional tape is convenient for.
Skip if: You already own a dependable laser measure or are working on a small layout where a quality tape handles everything comfortably.
Layout note: A laser measure improves measurement efficiency, but it does not establish the structural post locations for you. Determine the allowable beam spans first, then transfer those approved dimensions to the site.
Three Tools for Transferring the Post Layout
The laser handles longer measurements. A tape, square, and good marking tool handle the close-range work around beams, posts, batter boards, framing, and hardware.
Stanley FATMAX 25-Foot Tape Measure
A dependable tape remains faster than a laser for short measurements, offsets, post dimensions, hardware placement, and everyday framing checks.
Best for: Short layout measurements and general deck framing.
Swanson 7-Inch Speed Square
One of the highest-value tools in a deck-building kit for square marks, framing layout, checking cuts, and transferring dimensions around posts and beams.
Best for: Framing marks, square references, and everyday layout work.
Pica-Dry Longlife Automatic Pencil
Particularly useful when repeatedly transferring layout marks onto pressure-treated lumber, posts, beams, blocking, and other framing components.
Best for: Clear, repeatable jobsite layout marks.
Post Bases and Post Caps: Select the Connection First
Post bases and beam-to-post connectors are excellent examples of products that should not be selected from a generic shopping list.
The correct connector depends on the actual:
- post size
- beam configuration
- connection geometry
- concrete anchor or foundation detail
- treated-lumber exposure
- required corrosion protection
- design loads
- manufacturer-specified fasteners
Do not buy the hardware first and design the connection around it.
Determine the structural connection, identify the compatible connector, and then purchase that exact model and its specified fasteners.
Two Common Deck Post Connection Categories
These are verified BYS database links for common connector categories. Use them only after the required connection type and exact compatible model have been established.
Simpson Strong-Tie ZMAX Post Base
Used in compatible post-to-concrete details to locate and secure the post while providing the separation and connection specified for the selected assembly.
Verify before buying: Exact post-base model, post dimensions, anchor type, finish, exposure condition, and required fasteners.
Simpson Strong-Tie Post Cap
A purpose-built post cap can provide a defined beam-to-post connection where the selected connector matches the actual beam and post configuration.
Verify before buying: Beam plies, post dimensions, connector model, corrosion protection, and the manufacturer’s specified fasteners.
Deck Building Tools Guide
Post layout is only one stage of the build. Our complete tool guide covers measuring, layout, cutting, drilling, fastening, demolition, composite work, and which expensive tools are usually better rented.
Best for: Anyone planning to build more than the support system.
Deck Post Layout Decision Framework
Closer Post Spacing Makes Sense When:
- a smaller beam is more economical
- footing installation is easy
- open space below the deck is not important
- shorter structural spans are desirable
Wider Post Spacing Makes Sense When:
- the selected beam supports the required span
- larger footing reactions are accounted for
- clear space below the deck matters
- fewer excavations justify the larger beam cost
The goal is not maximum post spacing.
The goal is the most efficient complete structural system.
Frequently Asked Questions
How far apart should deck posts be?
Deck posts are commonly spaced around 6 to 8 feet apart in many residential layouts, but there is no universal spacing requirement. Structural posts should be located so the beam span between supports does not exceed the allowable span for the selected beam, species, joist span, cantilever, and design load.
Is 8 feet the standard deck post spacing?
No. Eight feet is common in residential construction, but it is not a universal code requirement. Some beam configurations require closer spacing while others can span farther.
Can deck posts be 10 feet apart?
Yes, some properly sized beams can span 10 feet between posts under suitable loading conditions. Other common beam configurations cannot. Check the applicable beam-span table.
Can deck posts be 12 feet apart?
Some larger beam configurations can span approximately 12 feet or more when carrying relatively modest loads, but many common residential beams cannot. Twelve-foot post spacing should never be assumed without verifying the beam design.
What is the maximum distance between deck posts?
There is no single maximum distance for all decks. Maximum spacing is established by the allowable beam span for the actual framing and loading conditions.
How many posts do I need for a 16-foot deck?
It depends on the maximum span of the beam. If the beam can span 8 feet, a simple 16-foot beam with no cantilever could use two 8-foot spans supported by three posts. If the allowable beam span is shorter, additional posts are required.
How many posts do I need for a 20-foot beam?
If the approved beam configuration can span 8 feet, divide 20 by 8 and round up to three beam spans. A simple beam with three spans requires four posts, assuming no cantilevers or other layout complications.
Does a larger beam allow wider post spacing?
Generally, yes. A deeper beam or additional beam ply can increase allowable span, provided the beam configuration is permitted for the applicable load and species.
Does wider post spacing require larger footings?
It can. Wider spacing often increases the tributary load carried by each post, which can increase the required footing bearing area.
Do joist cantilevers affect post spacing?
Yes. A joist cantilever adds deck area beyond the beam and can increase the load carried by the beam, potentially reducing its allowable span between posts.
Can the beam extend past the outside posts?
Yes. Prescriptive deck framing can permit beam cantilever beyond a bearing location, generally limited to one-fourth of the actual adjacent beam span when the other requirements are satisfied.
Should a deck beam sit on top of the post?
The beam needs proper structural bearing at the post. Common prescriptive solutions include bearing on top of the post with an approved connector or a properly detailed notched-post connection where permitted.
Are 6×6 posts required for every deck?
No. Six-by-six posts are common, but allowable post size depends on height, load, species, and the applicable prescriptive requirements.
The Backyard Standard Final Answer
Deck post spacing should not begin with a generic rule such as 6 feet, 8 feet, or 10 feet.
Start with the structure above the posts.
Determine the joist span and cantilever, select the beam, and use the applicable span table to determine how far that beam can safely span between supports.
Then place the posts within that limit and size the posts and footings for the loads they receive.
The simplest way to remember it:
Joists load the beam. The beam determines post spacing. The posts load the footings.
Continue with our Deck Beam Span Chart , Deck Beam Size Chart , Deck Cantilever Guide , and Deck Footing Count Guide .
Sources & Technical References
Technical references reviewed: September 2026
- International Code Council — 2024 IRC Chapter 5 — Deck beam spans, effective joist-span conditions, beam cantilevers, posts, and footing provisions.
- International Code Council — 2021 IRC Chapter 5 — Prescriptive deck framing tables and load-path provisions.
- American Wood Council — DCA 6 Prescriptive Residential Wood Deck Construction Guide — 2015 IRC-based supplemental deck framing guidance.
- American Wood Council — Residential Deck Resources
Code note: The IRC is a model code and DCA 6 is based on the 2015 IRC. Local jurisdictions may adopt different editions or amendments. The beam chart on this page is intentionally scoped to the stated Southern Pine, No. 2, 40 psf live-load / 10 psf dead-load planning condition; snow-load tables, cantilever conditions, local design criteria, and approved plans can produce different support spacing.
Related Deck Framing Guides
Deck Framing Guide
See how joists, beams, posts, footings, and connections work as one load path.
How Many Deck Posts Do I Need?
Turn allowable beam span and beam-run length into a practical support count.
Deck Post-to-Beam Connections
Provide proper beam bearing and restraint at each structural support post.
Deck Beam Span Chart
Determine how beam size, joist span, species, and load establish the maximum distance between posts.
Deck Beam Size Chart
Compare common built-up beam sizes and determine which configurations fit your structural layout.
Deck Joist Span Chart
See how joist length affects the load delivered to the beam and support system.
Deck Cantilever Guide
Understand joist and beam cantilevers and how they change structural loading and support locations.
How Many Footings Do I Need?
Turn the beam and post layout into an actual footing count for your deck.
Deck Footing Size Chart
See how post tributary load and soil-bearing capacity determine footing area.
Deck Framing Layout
Understand how joists, beams, posts, footings, and the ledger work together.
Deck Building Tools
See which layout and framing tools are worth buying, renting, or skipping.
