How Many Footings Do I Need for a Deck? Count, Spacing & Examples (2026)
The number of footings you need for a deck is usually determined by the number of structural support posts required beneath the deck’s beams. On a conventional post-and-footing deck, each structural post typically corresponds to one footing location.
How Many Footings Do I Need for a Deck? Calculator & Size Examples
The number of footings a deck needs is determined by its structural support system—not square footage alone. For a conventional post-and-footing deck, each structural support post normally creates a primary foundation location below it.
For preliminary planning, an attached 12×12 deck might use about 3 main footings, an attached 12×16 might use roughly 3–4, and an attached 16×20 might use roughly 3–5 or more. Freestanding versions can require substantially more because they typically need another independent support line instead of relying on a house ledger for vertical support.
Quick Answer: First determine the deck’s structural posts and support lines. Then count those primary foundation locations and add any separate support required for additional beams, stairs or landings, roofs, hot tubs, or other project-specific loads. Footing size is a separate calculation.
This page answers how many foundation support locations the deck needs. If you have not established the structural post layout yet, start with How Many Deck Posts Do I Need?.
Once the footing locations are known, use the Deck Footing Size Chart to determine required bearing area and the Deck Footing Calculator to estimate concrete.
How Many Deck Footings Do You Need? Quick Answer
The table below gives preliminary planning examples for conventional rectangular residential decks. These are not code-prescribed footing counts.
| Deck Size | Attached Example | Freestanding Example |
|---|---|---|
| 10×10 | About 2–3 main footings | About 4–6 main footings |
| 12×12 | About 3 main footings | About 6 main footings |
| 12×16 | About 3–4 main footings | About 6–8 main footings |
| 16×20 | About 3–5+ main footings | About 6–10+ main footings |
Planning examples only: Deck dimensions do not establish footing count. The actual number follows from the joist, beam, post, cantilever, load, and foundation design. Stairs, landings, roofs, hot tubs, additional beam rows, and other structural features can add foundation supports beyond these main-deck examples.
Deck Footing Count Calculator
Use this planner after you know how many structural posts are required along each beam. It totals the primary deck supports plus additional foundation locations for extra beam lines, stairs or landings, and dedicated structural loads.
If you do not know the post count yet, use the Deck Post Count Calculator first.
This attached-deck example uses 3 primary foundation locations beneath the exterior beam.
This calculator counts planned foundation support locations—it does not determine whether the framing is structurally adequate.
Post count, footing size, footing depth, soil bearing, frost protection, beam design, joist design, connections, and concentrated loads must still satisfy the applicable design requirements.
How Deck Footing Count Actually Works
For a conventional deck foundation, the easiest starting relationship is:
For the main deck framing, one structural post commonly corresponds to one foundation support location in a conventional post-and-footing system.
But total foundation count can exceed the number of posts under the main exterior beam.
A complete deck may also have:
- a second beam line on a freestanding deck
- an additional interior beam
- structurally supported stair landings
- separate support for a roof or covered structure
- dedicated support for a hot tub or other concentrated load
- multiple deck levels
- other project-specific foundation locations
Important distinction: The Deck Post Count Guide determines the structural posts required by the beam system. This page takes the next step and considers the complete foundation-support count.
Where Footing Count Fits in the Deck Load Path
Footings are near the bottom of the structural load path. That is why footing count should not be the first design decision.
The framing above determines where concentrated reactions reach the foundation.
For a conventional system:
joists load beams → beams load posts → posts load footings → footings distribute those reactions into soil.
Don’t start by asking where to dig holes. Establish the framing system first. The main footing locations are an output of that design.
Attached vs. Freestanding Deck Footing Count
Whether the deck uses an approved structural ledger is one of the biggest reasons two decks with identical dimensions can need very different numbers of main footings.
Attached 12×16 Deck
In this simplified example, the approved ledger provides vertical support at the house side and one exterior beam uses three structural posts.
Freestanding 12×16 Deck
This simplified freestanding example replaces the ledger’s vertical support with another independent beam and three additional posts.
Same 12×16 footprint. Different foundation count. These diagrams illustrate why deck dimensions alone cannot determine how many footings are required.
How Many Footings for Common Deck Sizes?
Homeowners often search by deck size, so the examples below provide useful preliminary ranges while preserving the structural distinction between deck dimensions and support design.
A compact attached deck may use roughly two or three main exterior-beam supports when the selected framing permits that layout.
A comparable freestanding layout may require approximately four to six main foundation locations across two support lines.
A simple attached 12×12 example can use one exterior beam supported by three posts, producing three main footing locations.
A freestanding version using two similar three-post beams would have six main footing locations.
A conventional attached 12×16 deck may use roughly three or four main footings depending on the allowable span of the exterior beam.
A comparable freestanding system using two support rows may use roughly six to eight.
These are illustrative planning ranges—not footing schedules. The actual post layout must be determined from the beam design before the footing count is finalized.
How Many Footings Does a 12×12 Deck Need?
For preliminary planning, a conventional attached 12×12 deck might use about three main footing locations beneath one exterior beam.
A comparable freestanding 12×12 deck might use about six main footing locations if it uses two independent three-post support beams.
Those numbers are examples, not rules.
A different beam size, joist orientation, allowable beam span, beam cantilever, load condition, or foundation system can produce a different count.
How Many Footings Does a 12×16 Deck Need?
A conventional attached 12×16 deck may use roughly 3–4 main footings beneath one exterior beam. A comparable freestanding design using two similar support rows may use roughly 6–8 main footings.
Why the range?
The exterior beam still has to satisfy its allowable span between structural posts.
Under one defined Southern Pine framing condition, for example, a 16-foot beam line using a beam with a 7′-4″ allowable span requires at least three beam spans and four posts. A qualifying beam capable of more than an 8-foot span can potentially use two 8-foot spans and three posts.
The deck remained 12×16 in both cases. The beam design changed the post count, and the post count changed the primary footing count.
Use How Many Deck Posts Do I Need? for the complete beam-span-to-post-count calculation.
How Many Footings Does a 16×20 Deck Need?
For preliminary planning, an attached 16×20 deck might use roughly 3–5 or more main beam footings, while a freestanding design can require roughly 6–10 or more across multiple independent support lines.
Those ranges become less precise as decks become larger because the framing layout itself becomes more important.
A 16-foot projection can affect:
- joist span
- joist cantilever
- beam location
- tributary width
- beam size
- number of beam lines
- post reactions
- footing size
Do not use “4 footings for a 16×20 deck” or any similar fixed number as a design rule. Establish the framing system first and count the resulting structural support locations.
What Determines How Many Deck Footings You Need?
| Design Variable | Why It Changes Footing Count |
|---|---|
| Attached vs. freestanding | A freestanding deck generally needs independent support on the house side instead of relying on a ledger. |
| Number of beam lines | Every additional post-supported beam can add another row of foundation locations. |
| Beam length | Longer beam runs may require additional supported spans. |
| Allowable beam span | Shorter allowable spans require more posts along the same beam line. |
| Joist span | Longer joists can increase beam loading and change allowable beam span. |
| Cantilevers | Permitted overhangs can change where exterior supports are located. |
| Stairs and landings | Some configurations require foundation support beyond the main deck rectangle. |
| Roofs / hot tubs / heavy features | Concentrated or additional loads may require separately designed support locations. |
| Alternative foundation system | Approved piers, piles, or other systems can use different support arrangements than conventional concrete footings. |
How Post Count Determines Main Footing Count
For the main beam system, the relationship is straightforward:
Structural beam posts ≈ primary foundation support locations
But the beam design should establish the posts. Do not decide that a deck needs four footings and then force the beam layout to fit those four locations.
The structural sequence is:
The Deck Post Count Calculator handles that upstream calculation.
This separation is important because footing count and footing size answer different questions.
Footing Count vs. Footing Size: Don’t Confuse Them
How Many Footings?
Determined primarily by the number and arrangement of structural foundation support locations.
Output: where foundations are needed.
How Big Should Each Footing Be?
Determined by the reaction delivered to that support, soil-bearing capacity, and applicable foundation requirements.
Output: required bearing area and footing dimensions.
Fewer footings do not automatically mean smaller or cheaper foundations. Removing supports can increase the reaction carried by each remaining post and footing.
Once the locations are established, continue with the Deck Footing Size Chart.
Why Tributary Area Matters After You Count the Footings
Two footings on the same deck do not necessarily carry the same load.
Each structural support receives load from a portion of the deck called its tributary area.
For a simple interior support along a beam, the tributary width along the beam is influenced by half the adjacent beam span on each side. The tributary depth depends on the joist system delivering load to that beam.
That is why an interior post can carry a larger reaction than an end post.
Count tells you how many support locations exist. Tributary area helps determine how much load reaches each one.
Use the Deck Tributary Area Calculator to continue the load-path calculation.
Can a Bigger Beam Reduce the Number of Footings?
Potentially.
If a larger or stronger beam can span farther between posts under the actual loading condition, fewer structural posts—and therefore fewer main foundation locations—may be possible along that beam.
| Layout Choice | Framing Effect | Foundation Effect |
|---|---|---|
| More posts | Shorter beam spans | Load distributed among more foundation locations |
| Fewer posts | Longer beam spans require adequate beam capacity | Remaining supports can carry larger reactions |
A layout with fewer holes can require:
- a larger beam
- larger or taller posts
- stronger connections
- larger individual footing bearing areas
- more difficult material handling
Foundation efficiency is not measured by the fewest holes. The goal is an efficient complete load path.
How Far Apart Should Deck Footings Be?
There is no universal rule that deck footings should be exactly 6 feet, 8 feet, or another single distance apart.
For a conventional beam-and-post deck:
Footing spacing follows post spacing, and post spacing follows allowable beam span.
Allowable beam span depends on the beam size and plies, lumber species and grade, supported joist span, cantilever condition, design load, and applicable design provisions.
Use the Deck Footing Spacing Guide for the complete spacing workflow and the Deck Post Spacing Chart for the beam-to-post relationship.
Can Cantilevers Change the Number of Footings?
Yes. A permitted beam cantilever can move the outside support posts inward from the ends of the beam.
Likewise, a joist cantilever can move the supporting beam inward from the deck edge.
That means the visible deck dimensions are not necessarily the same as:
- joist structural span
- beam supported span
- distance between outside posts
- distance between outside footing centers
Do not subtract an arbitrary overhang to eliminate a footing. Cantilever limits are part of the structural design and must be verified independently.
See the Deck Cantilever Guide before moving support locations inward.
Do Deck Stairs Need Additional Footings?
They can.
The primary footing count beneath the deck beams does not automatically represent every foundation support needed for the completed deck.
Deck stairs need stable lower support, and some configurations can add:
- landing foundations
- posts supporting an elevated landing
- additional beam or header supports
- foundation locations created by multi-flight stairs
The exact requirement depends on the stair and landing design.
When using the Footing Count Calculator above, add stair or landing foundation locations only after the stair design establishes that those supports are required.
Continue with the Deck Stairs Guide for stair framing and support planning.
Hot Tubs, Roofs & Heavy Loads Can Change the Foundation Plan
An ordinary open-deck footing layout should not automatically be reused when the project adds substantial concentrated or additional loads.
Examples include:
- hot tubs
- deck roofs
- covered porches
- pergolas that impose structural loads on the deck
- masonry fireplaces
- large outdoor kitchens
- heavy planters
- multiple deck levels
- unusual snow loads
These features can change:
- joist loading
- beam loading
- post reactions
- support locations
- footing size
- the suitability of a prescriptive deck design
Plan heavy features before the foundations are built. The correct solution may involve a different framing system or dedicated support—not simply “one extra footing.”
Do All Decks Need Conventional Concrete Footings?
No.
Some qualifying deck configurations can use other approved foundation systems or prescriptively permitted alternatives where all applicable conditions are satisfied.
Depending on the project and local approval, foundation systems can include:
- conventional poured concrete footings and piers
- approved precast systems
- helical piles or piers
- other proprietary foundation systems
- limited low-deck support systems where permitted
A very low freestanding deck is one condition where alternative support provisions may be relevant, but “ground-level” does not automatically mean “no foundation requirements.”
See How to Build a Ground-Level Deck for low-deck planning.
Do Helical Piers Change the Number of Supports?
Helical piles or piers can replace conventional concrete foundation locations in an approved foundation system, but they do not eliminate the structural reactions that must reach the ground.
Their number, capacity, spacing, location, installation, and connection details should follow the approved system design.
Do not assume a one-for-one substitution solely from a concrete-footing layout. The alternative foundation system needs to be designed or approved for the reactions it will carry.
How Deep Do Deck Footings Need to Be?
Footing depth and footing count are separate requirements.
Footing count identifies support locations. Bearing area addresses vertical load distribution. Foundation depth and frost protection address other structural and site requirements.
Do not use a single national footing-depth number as a universal rule.
Required depth or frost protection depends on factors including:
- locally adopted code
- local frost conditions
- deck attachment and configuration
- foundation system
- soil and site conditions
Confirm the applicable requirement with the authority having jurisdiction before excavation.
Footings, Piers & Posts: What’s the Difference?
| Component | Primary Function |
|---|---|
| Footing | Provides bearing area that distributes structural reaction into the soil. |
| Concrete pier | Transfers load vertically between the deck/post and the footing or bearing surface. |
| Post | Transfers beam reaction downward into the foundation system. |
| Post base | Provides the specified post-to-concrete connection where applicable. |
| Helical pile / pier | Transfers structural load into suitable soil through an approved proprietary foundation system. |
Deck Footing Planning Workflow
- Choose the deck dimensions.
- Determine whether the deck will be attached or freestanding.
- Choose the joist direction and spacing.
- Determine allowable joist span.
- Establish the required beam line or beam lines.
- Select the beam configuration and determine allowable beam span.
- Lay out the structural posts.
- Count the main beam foundation locations.
-
Add separately required supports.
Include additional beams, stairs/landings, roofs, hot tubs, or other structural features where the design requires them. - Determine the reaction or tributary load at each support.
- Size each footing for load and allowable soil-bearing pressure.
- Determine footing depth and frost protection.
- Calculate concrete quantities.
- Verify the complete design under the locally adopted code before digging.
The mistake to avoid is starting at Step 8. Footing count is an output of the framing and support design—not the first design input.
Common Deck Footing Count Mistakes
1. Using Square Footage Alone
There is no dependable “one footing per X square feet” rule for conventional deck framing.
2. Automatically Spacing Footings Every 8 Feet
Footing locations normally follow the structural posts, and post spacing follows the allowable beam span.
3. Counting Only the Exterior Beam
Freestanding decks, additional beam rows, landings, and other structural features can create additional foundation locations.
4. Confusing Footing Count With Footing Size
Adding more bearing area does not allow an undersized beam to span farther between posts.
5. Assuming Every Footing Carries the Same Load
Interior and end supports can have different tributary areas and reactions.
6. Using a Bigger Beam Without Rechecking the Foundations
A stronger beam may allow fewer supports, but the remaining posts and footings can carry larger reactions.
7. Forgetting Stairs and Landings
The main rectangular deck support system is not necessarily the entire foundation plan.
8. Adding a Hot Tub or Roof Later
Heavy features can materially change the framing and foundation design.
9. Treating Ground-Level as Foundation-Free
Low decks can qualify for different provisions in some configurations, but height alone does not eliminate structural or foundation requirements.
Once You Know the Footing Count, Do These Two Calculations
Size Each Footing
Convert the reaction at each support and the applicable soil-bearing capacity into the required footing bearing area.
Open Footing Size Chart →Calculate Concrete
Once footing dimensions are established, estimate concrete volume and bag quantities for the foundation work.
Open Footing Calculator →Correct sequence: support layout → footing count → support reactions → footing size → concrete quantity.
Not Sure Your Deck Footing Layout Works?
Foundation mistakes become difficult and expensive to correct after excavation and concrete placement.
Professional review becomes especially valuable when the project includes:
- a large or elevated deck
- multiple beam lines
- difficult access or sloped terrain
- unusual soil conditions
- a roof or covered structure
- a hot tub or other concentrated load
- complex stairs or elevated landings
- an alternative foundation system
If you would rather compare the proposed framing and foundation approach with a professional deck contractor before digging, you can request local contractor options through Angi.
Compare Local Deck Contractors →
Disclosure: The Backyard Standard may earn a commission if you submit a service request through this link, at no additional cost to you.
Deck Footing Count FAQ
How many footings do I need for a deck?
For a conventional post-and-beam deck, the main footing locations generally correspond to the structural posts supporting the beam system. Then add any separate foundation supports required for additional beams, stairs or landings, roofs, heavy loads, or other structural features.
How many footings does a 10×10 deck need?
For preliminary planning, a conventional attached 10×10 deck might use roughly two or three main exterior-beam footings. A freestanding design can require roughly four to six across two support rows. Actual framing controls the count.
How many footings does a 12×12 deck need?
A simple attached 12×12 example may use about three main footing locations beneath one exterior beam. A comparable freestanding example using two three-post beams may use six. Other valid layouts can produce different counts.
How many footings does a 12×16 deck need?
A conventional attached 12×16 deck may use roughly three or four main footing locations depending on the exterior beam design. A comparable freestanding layout using two similar support rows may use roughly six to eight.
How many footings does a 16×20 deck need?
For preliminary planning, an attached 16×20 deck might use roughly three to five or more main beam footings, while a freestanding layout can require roughly six to ten or more. Larger decks are especially dependent on the actual joist and beam arrangement.
How many footings does a freestanding deck need?
Freestanding decks commonly require more foundation locations than comparable ledger-attached decks because the house side also needs independent vertical support. A simple rectangular freestanding layout often uses two post-supported beam lines.
Can a 12×16 deck have only three footings?
Potentially. A valid ledger-attached 12×16 layout can use one three-post exterior beam when the joists, beam, posts, ledger, connections, cantilevers, footing capacities, and complete structural system support that arrangement.
How far apart should deck footings be?
There is no universal footing spacing. In a conventional post-and-beam system, footing locations normally follow the structural posts, and post spacing follows the allowable beam span.
Does every deck post need a footing?
Every structural post needs an approved load path into the ground or another approved supporting system. In a conventional post-and-footing deck, that normally means a foundation support beneath each structural post.
Can bigger footings let me use fewer posts?
Not by themselves. A larger footing can provide greater bearing area, but the beam above must still be capable of spanning the increased distance between structural supports.
Can a bigger beam reduce the number of footings?
Potentially. If a larger or stronger beam is permitted to span farther under the actual loading condition, it may require fewer posts. The remaining posts and footings can then carry larger reactions and must be checked accordingly.
Do deck stairs need separate footings?
They can. Stairs need stable lower support, and elevated landings or some stair configurations can require foundation support beyond the primary deck-beam footing layout.
Do I need more footings for a hot tub?
A hot tub creates a substantial concentrated load and can require a specifically designed framing and foundation system. Do not assume the ordinary open-deck footing layout is adequate.
Do deck footings have to go below the frost line?
Frost-protection requirements depend on the deck configuration, locally adopted code, foundation system, and site conditions. Confirm the required foundation depth or approved frost-protection method locally.
Are deck blocks considered footings?
Precast deck blocks are an alternative support system used only in qualifying configurations. They are not a universal substitute for conventional below-grade deck foundations.
Technical References
Technical references reviewed: September 2026
- International Code Council — 2024 IRC Chapter 5 / Exterior Deck Provisions
- International Code Council — 2024 IRC Chapter 4 / Foundations
- American Wood Council — Residential Deck Resources
- American Wood Council — DCA 6 Prescriptive Residential Wood Deck Construction Guide
Code note: The IRC is a model code and local adoption and amendments control. AWC DCA 6 is based on the 2015 IRC and should not be treated as the current locally adopted code for every project. Prescriptive deck provisions also have defined scope limits; unusual loads and configurations may require project-specific design.
How Many Footings Do You Need for a Deck? Final Answer
The number of deck footings you need follows the complete structural support layout—not deck square footage alone.
For preliminary planning:
- 12×12 attached: about 3 main footings can be a reasonable example
- 12×16 attached: roughly 3–4 main footings
- 16×20 attached: roughly 3–5 or more
- 12×16 freestanding: roughly 6–8 main footings across two support rows
Those numbers are illustrative ranges—not code-prescribed footing counts.
The reliable workflow is:
joists → beams → posts → main footing locations → additional structural supports → footing size → soil
First establish the structural post layout using How Many Deck Posts Do I Need?. Then account for any additional foundation support required by the rest of the project.
After the total support layout is established, use the Deck Tributary Area Calculator and Deck Footing Size Chart to determine what each footing must support.
Related Deck Foundation & Framing Guides
How Many Deck Posts Do I Need?
Calculate structural post count from beam length and allowable beam span.
Deck Footing Spacing Guide
Understand how post locations and beam spans establish footing spacing.
Deck Tributary Area Calculator
Estimate the deck area contributing load to individual posts and footings.
Deck Footing Size Chart
Convert support reactions and soil-bearing assumptions into required bearing area.
Deck Footing Calculator
Estimate concrete volume after footing dimensions have been established.
How to Build a Freestanding Deck
See how independent support lines change the framing and foundation system.
That means footing count cannot be determined from deck square footage alone. A 10×10, 12×12, 12×16, or 16×20 deck can require different numbers of footings depending on the framing layout.
For example, a 12×16 deck might use three main footings in one framing configuration and six or more in another. The difference depends on whether the deck attaches to the house or is freestanding, how many beam lines it needs, how far each beam can span between posts, and whether the beams or joists cantilever beyond their supports.
The correct way to determine how many footings you need for a deck is to follow the structural load path:
decking → joists → beams → posts → footings → soil
Quick Answer: Determine the deck’s beam layout and allowable beam span between support posts. Then count the posts required beneath each beam. For a conventional post-and-footing foundation, those post locations establish the primary footing count. Footing size is a separate calculation based on the reaction at each support, tributary area, soil-bearing capacity, and applicable code requirements.
This guide answers the quantity question. Use the Deck Footing Spacing Guide for support layout and the Deck Footing Size Chart for individual footing dimensions.
How Many Deck Footings Do You Need? Quick Count Guide
If you are still planning the deck, the table below shows why there is no universal footing count based on deck dimensions alone. The number of footings depends on the framing system, beam layout, allowable beam span, and number of structural posts required.
| Deck Configuration | Common Support Layout | What Controls Footing Count? |
|---|---|---|
| Attached deck | House ledger + exterior beam | Posts required beneath the exterior beam |
| Freestanding deck | Independent support lines | Total posts required beneath all supporting beams |
| Deep deck | May require another beam line | Joist span limits + beam arrangement |
| Long deck | More beam spans may be required | Beam size + allowable beam span + beam length |
| Deck with hot tub or roof | May require dedicated/additional supports | Concentrated loads + project-specific design |
| Very low freestanding deck | May qualify for an approved alternative foundation | Configuration + locally adopted code |
The key point: Deck dimensions tell you how much deck must be supported. The beam and post layout determines how many footing locations are needed.
The Basic Rule: Footings Follow Structural Posts
For a conventional residential deck supported by posts and beams, the starting relationship is simple:
1 structural post ≈ 1 footing location
So the more useful question is usually not “How many footings does a 16×20 deck need?” but “How many posts does my beam layout require?”
Once the beams and posts are designed, the primary footing count becomes much easier to identify. This does not mean every footing will necessarily be the same size. Interior and end supports can carry different reactions and tributary areas.
What Determines How Many Deck Footings You Need?
Attached vs. Freestanding Construction
A conventional attached deck can use an approved structural ledger to support the house side of the joists, with a post-supported beam toward the outside. A freestanding deck needs an independent support system instead of relying on the house ledger for vertical support, so a simple freestanding layout commonly has more main footing locations.
Joist Span and Beam Lines
Joists can span only so far based on size, species, grade, spacing, loading, and framing configuration. A deeper deck may require a different beam location or an additional beam line. Use the Deck Joist Span Chart before deciding how many beam lines are needed.
Beam Size and Allowable Beam Span
The beam must carry the joist load between posts. A beam configuration capable of a longer allowable span can sometimes use fewer posts along the same beam run. Check both the Deck Beam Size Chart and Deck Beam Span Chart.
Beam Length
Once allowable post-to-post beam span is known, the total supported beam length determines how many spans and posts are required.
Beam and Joist Cantilevers
Permitted cantilevers can change support locations, but they are not a shortcut to arbitrary post spacing. Verify the actual cantilever condition with the Deck Cantilever Guide.
Additional Loads
Hot tubs, roofs, masonry, large outdoor kitchens, unusual snow conditions, and other concentrated or nonstandard loads can require a different framing and foundation design rather than simply adding a generic footing.
How to Calculate the Number of Footings for a Simple Deck Beam
For a preliminary straight-beam layout with a support at each end and no beam cantilever:
- Find the allowable beam span for the actual beam configuration and supported joist span.
- Divide the beam length by that allowable span.
- Round up to the next whole number to get the minimum number of beam spans.
- Add 1 to get the number of posts.
- For a conventional post-and-footing beam, the post count normally becomes the footing count for that beam.
Beam spans = Round Up (supported beam length ÷ allowable beam span)
Posts = beam spans + 1
Primary footings ≈ structural posts
Important: This is a layout shortcut, not a substitute for the applicable span table or engineered design. End supports, cantilevers, beam continuity, loading, and actual construction details still matter.
Example: 20-Foot Beam With an 8-Foot Allowable Span
Suppose a preliminary design has a 20-foot supported beam length and the selected beam configuration is permitted to span no more than 8 feet between supports.
20 ÷ 8 = 2.5 → round up to 3 beam spans
Three consecutive spans require four supports:
Post — Span — Post — Span — Post — Span — Post
The simplified layout therefore has 3 beam spans, 4 posts, and 4 primary footing locations.
The 8-foot span is an assumption for this math example—not a universal deck-post-spacing rule. Your actual allowable beam span must come from the applicable beam table or project-specific design.
What If the Beam Cantilevers Past the End Posts?
A valid beam cantilever can move the outside posts inward, so a footing-count formula based on total beam length can be misleading.
Supported distance between outside supports = total beam length − left overhang − right overhang
For example, a 20-foot beam with a 1-foot overhang beyond each outside support has 18 feet between those outside support locations. The interior support layout must then satisfy the allowable spans while the overhangs themselves are separately verified.
Do not assume a generic beam-cantilever allowance. Beam cantilever design depends on the applicable rules and loading; use the Deck Cantilever Guide or project-specific design.
Attached vs. Freestanding Deck: Why Footing Count Can Change Dramatically
| Feature | Attached Deck | Freestanding Deck |
|---|---|---|
| House-side vertical support | Approved ledger in a conventional layout | Independent support system |
| Simple rectangular layout | Often one post-supported exterior beam | Often two post-supported beam lines |
| Relative main footing count | Often lower | Often higher |
If an attached layout uses one exterior beam with three structural posts, that beam has three primary footing locations. If a comparable freestanding layout uses two three-post beams, it has six primary footing locations.
That is an illustration, not a universal 3-vs.-6 rule. Actual beam count and post spacing still depend on the structural design.
Same 12×16 Deck Size, Different Footing Count
This is the easiest way to see why deck dimensions alone do not determine footing count. Both examples below use the same 12×16 deck footprint. The difference is how the deck is supported.
Attached 12×16 Deck
House side: supported by an approved structural ledger in this example.
Outer side: one beam supported by three posts.
Freestanding 12×16 Deck
House side: supported by its own beam and posts.
Outer side: supported by a second beam and posts.
Important: These are simplified framing examples, not universal footing counts for every 12×16 deck. The actual number still depends on joist span, beam size and allowable beam span, cantilevers, loading, and the complete structural design.
How Many Footings for Common Deck Sizes?
These examples capture common homeowner searches, but they are not footing schedules or permit-design recommendations. They simply show how different support arrangements can produce different counts for the same deck size.
| Deck Size | Illustrative Attached Layout | Illustrative Freestanding Layout |
|---|---|---|
| 10×10 | One 3-post beam → 3 main footings | Two 3-post beams → 6 main footings |
| 12×12 | One 3-post beam → 3 main footings | Two 3-post beams → 6 main footings |
| 12×16 | One 3-post beam → 3 main footings | Two 3-post beams → 6 main footings |
| 16×20 | Example exterior support line only; actual count depends strongly on joist/beam design | Multiple independent support lines may be required; design first |
Why the 16×20 row is intentionally less specific: a 16-foot projection can materially affect joist and beam arrangement. Publishing a generic “4 attached / 8 freestanding” answer without defining the actual joists, beams, species, grade, spacing, load, and support geometry would imply more certainty than the deck dimensions provide.
How Many Footings Does a 12×12 Deck Need?
There is no universal number. A simple illustrative attached 12×12 deck can use one exterior beam supported by three posts, producing three main beam footing locations. A comparable freestanding example using two three-post support lines would have six.
Other structurally valid layouts can produce different counts. Verify the joist span, beam span, cantilevers, post capacity, and footing design rather than treating 3 or 6 as a rule for every 12×12 deck.
How Many Footings Does a 12×16 Deck Need?
A 12×16 attached deck can potentially use three main footing locations beneath one exterior beam when the complete framing design allows that three-post beam layout. A freestanding example using two equivalent three-post beam lines would have six main footing locations.
The key condition is the beam: if the selected beam cannot safely span between those three posts under the actual supported joist span and loading, another post may be required.
How Many Footings Does a 16×20 Deck Need?
A 16×20 deck does not have a reliable footing count based on dimensions alone. The 16-foot projection is especially important because it can change joist span, beam location, tributary width, and even the number of required beam lines.
Design the joist-and-beam system first. Then count the structural posts beneath the resulting beam lines. A freestanding version can require substantially more foundation supports than an attached version because it needs independent support on the house side as well.
Can a 12×16 Deck Have Only 3 Footings?
Potentially, yes. A conventional ledger-attached deck could use one exterior beam with three posts if the complete structural system supports that layout.
- The joists must be permitted to span from the ledger to the beam.
- The selected beam must be permitted to span between the three posts.
- Any joist or beam overhang must be within its allowable limit.
- The posts must be adequate for their reactions and heights.
- Each footing must be sized for its reaction and allowable soil-bearing pressure.
- The ledger and its connections must be permitted and properly designed.
Three footings are enough only when the entire structural system makes the three-post layout valid.
Footing Count vs. Footing Size: Don’t Confuse the Two
There are two separate foundation questions:
1. How many support locations does the deck need?
Beam layout and allowable beam spans help establish the post—and therefore primary footing—locations.
2. How large must each footing be?
The reaction at each support and allowable soil-bearing pressure determine the required bearing area, subject to the applicable prescriptive requirements.
Reducing the number of supports can increase the reaction at the remaining supports. A larger beam may therefore allow fewer posts while the remaining footings need greater bearing area.
Continue with the Deck Footing Size Chart once the support layout is established.
What Is Tributary Area—and Why Does It Matter?
Tributary area is the portion of deck area contributing gravity load to a particular support. It helps explain why two footings on the same deck can carry different reactions.
For a simple interior post along a beam, the tributary width along the beam is generally influenced by half the adjacent beam span on each side. The tributary depth is determined by the portion of the joist system delivering load to that beam.
That is why an interior support often carries more load than an end support: it receives load from framing on both sides.
See the Deck Tributary Area Guide for the full load-path explanation.
Why Fewer Footings Can Mean Larger Footings
Imagine the same beam run supported in two valid ways:
| Layout | Support Effect | Foundation Effect |
|---|---|---|
| More posts | Shorter beam spans | Load distributed among more footing locations |
| Fewer posts | Longer beam spans require adequate beam capacity | Remaining supports can carry larger reactions |
Foundation efficiency is not measured by the fewest holes. The goal is a coordinated framing and foundation design.
How Far Apart Should Deck Footings Be?
There is no universal rule that deck footings should be exactly 6 feet, 8 feet, or another single distance apart.
Footing spacing normally follows post spacing, and post spacing follows allowable beam span. Beam span depends on beam size and plies, lumber species and grade, supported joist span, cantilever conditions, loading, and the applicable design provisions.
Use the Deck Footing Spacing Guide for the complete spacing workflow and the Deck Post Spacing Chart for the beam-to-post relationship.
Can a Bigger Beam Reduce the Number of Footings?
Sometimes. If a larger or stronger beam is permitted to span farther between posts under the same loading condition, it can reduce the number of support locations along that beam.
The tradeoff is that larger beams cost and weigh more, and the remaining posts and footings can carry larger reactions. Post size, post height, connections, and footing bearing area must still work.
Do All Decks Need Conventional Concrete Footings?
No. Some deck configurations can use other approved foundation systems, including proprietary or prescriptively permitted systems where all applicable conditions are satisfied.
Very low freestanding decks are the condition most likely to qualify for simplified or alternative support provisions, but “ground-level” does not automatically mean “no footings.” Attachment, height, area, beam/post use, soil, and the locally adopted code still matter.
For low-deck planning, see How to Build a Ground-Level Deck.
Do Helical Piers Change the Number of Supports?
Helical piles or piers can replace conventional concrete foundation locations in an approved system, but they do not eliminate the structural reactions that must reach the ground.
The number, capacity, location, and installation of helical supports should follow the approved system design rather than assuming a one-for-one substitution without verification.
How Deep Do Deck Footings Need to Be?
Footing depth and footing count are separate requirements. Bearing area distributes vertical load; foundation depth and frost protection address other site and code requirements.
Do not use a single national depth as a universal rule. Required frost protection and foundation depth depend on the locally adopted code, deck configuration, and site conditions. Confirm the applicable requirement with the authority having jurisdiction.
Do Deck Stairs Need Additional Footings?
They can. The main beam footing count does not automatically include all support required for stairs. Stringers need stable bearing at the bottom, and landings or certain stair configurations can require additional foundation support.
Continue with the Deck Stairs Guide when planning the stair system.
Hot Tubs, Roofs & Other Heavy Loads Can Change the Foundation Plan
Do not automatically reuse an ordinary open-deck footing layout when adding substantial concentrated or additional loads.
- Hot tubs
- Deck roofs or covered porches
- Masonry fireplaces
- Large outdoor kitchens
- Heavy planters
- Unusual snow loading
- Multiple deck levels
- Large stair landings
Plan heavy features before the foundation is built. They can change beam, post, and footing reactions rather than simply requiring “one extra footing.”
Footings, Piers & Posts: What’s the Difference?
| Component | Primary Function |
|---|---|
| Footing | Spreads structural reaction over sufficient soil-bearing area |
| Concrete pier | Transfers load vertically between the deck/post and footing or bearing surface |
| Post | Transfers beam reaction downward into the foundation system |
| Post base | Provides the specified post-to-concrete connection where applicable |
Common Deck Footing Count Mistakes
- Using square footage alone: there is no dependable “one footing per X square feet” rule.
- Assuming 8-foot spacing: allowable beam span, not a generic spacing number, controls the post layout.
- Counting posts before sizing the beam: reliable post spacing requires an actual beam condition.
- Forgetting house-side support on a freestanding deck: removing the ledger does not remove the load.
- Ignoring joist span: one exterior beam does not work if the joists cannot reach it within their allowable span.
- Assuming every footing is identical: support reactions can differ.
- Using cantilever without checking it: moving posts inward changes geometry but does not erase cantilever limits.
- Forgetting stairs and heavy features: the main rectangle is not always the complete foundation system.
Deck Footing Planning Workflow
- Choose the deck dimensions.
- Determine whether it will be attached or freestanding.
- Choose joist direction and spacing.
- Determine allowable joist span.
- Establish the required beam line or beam lines.
- Determine the load condition carried by each beam.
- Select the beam size/configuration.
- Determine allowable beam span between posts.
- Lay out posts, including any verified cantilever.
- Count structural support locations.
- Determine reaction/tributary area at each support.
- Size each footing for the load and allowable soil-bearing pressure.
- Confirm foundation depth and frost requirements.
- Add support required for stairs, landings, roofs, hot tubs, or other loads.
- Verify the complete plan under the locally adopted code before digging.
The mistake to avoid is starting at Step 10. Footing count is an output of the framing design, not the first design input.
Useful Tools for Laying Out Deck Footings
As an Amazon Associate, The Backyard Standard earns from qualifying purchases, at no additional cost to you.
Once the structural plan establishes footing centers, these verified BYS database tools can help transfer the dimensions to the site.
Stanley FATMAX 25-Foot Tape
Useful for basic footing-center and framing measurements.
Bosch BLAZE Pro GLM165-40
Useful for longer deck dimensions, beam runs, and preliminary support layout.
Most homeowners do not need professional survey/elevation equipment for a single deck. See the Deck Building Tools Guide for the broader buy-vs.-rent discussion.
Once You Know the Footing Count, Calculate the Concrete
Footing count is only the first foundation quantity. After the design establishes each footing’s dimensions, use the Deck Footing Calculator to estimate concrete volume and bag quantities.
Framing design → footing locations → support reactions → footing size → concrete quantity
Frequently Asked Questions
How many footings do I need for a deck?
For a conventional post-and-beam deck, the number of primary footing locations generally corresponds to the structural posts required beneath the beams. Determine the beam layout and allowable beam spans first, then count the posts.
How many footings does a 10×10 deck need?
There is no universal count. As an illustration, one attached layout could use a three-post exterior beam and three main footings, while a freestanding example with two three-post support lines would have six. The actual framing design controls.
How many footings does a 12×12 deck need?
An illustrative attached layout can use three main footing locations beneath one exterior beam, while a comparable freestanding layout can use six. Other valid designs can produce different counts.
How many footings does a 12×16 deck need?
A simple attached 12×16 deck can potentially use three main footing locations when the joist and beam design permits one three-post exterior beam. A comparable freestanding example can use six. Verify the actual beam spans and support reactions.
How many footings does a 16×20 deck need?
Deck dimensions alone do not provide a reliable answer. A 16-foot projection can change the joist span and beam arrangement, so establish the framing system before assigning a footing count.
How many footings do I need for a freestanding deck?
Freestanding decks commonly need more foundation supports than comparable ledger-attached decks because they require independent support on the house side as well as the outer side. The actual number follows the beam and post layout.
Can a 12×16 deck have only three footings?
Potentially, in a valid ledger-attached layout using one three-post exterior beam. The joists, beam, posts, footings, ledger, connections, and any cantilevers all have to support that configuration.
How far apart should deck footings be?
There is no universal spacing. Footing locations normally follow the structural posts, and post spacing follows the allowable beam span for the actual beam and load condition.
Can bigger footings let me use fewer posts?
Not by themselves. A larger footing can provide more bearing area, but the beam above must also be capable of spanning the increased distance between supports.
Can a bigger beam reduce the number of footings?
Potentially. If the larger beam has a greater allowable span under the actual load condition, it can reduce the required posts along that beam. Remaining supports may carry larger reactions.
Does every deck post need a footing?
Every structural post needs an approved load path into the ground or another approved supporting system. On a conventional post-and-footing deck, that normally means a foundation support beneath each structural post.
Do deck stairs need separate footings?
Stairs need stable lower support, and landings or some stair configurations can require additional foundation support beyond the main deck footing layout.
Do I need more footings for a hot tub?
A hot tub creates a substantial concentrated load and commonly requires a specifically designed support system. Do not assume the ordinary open-deck footing layout is adequate.
Do deck footings have to go below the frost line?
Frost-protection requirements depend on the deck configuration, locally adopted code, and site conditions. Confirm the required foundation depth or approved frost-protection method locally.
Are deck blocks considered footings?
Precast deck blocks are an alternative support system in limited configurations, not a universal substitute for conventional below-grade footings. Use them only where the applicable code and deck design permit that system.
Technical References
Technical references reviewed: September 2026
- International Code Council — 2024 IRC Chapter 5 / Exterior Deck Provisions
- International Code Council — 2024 IRC Chapter 4 / Foundations
- American Wood Council — Residential Deck Resources
- American Wood Council — DCA 6 (2015 IRC-Based)
Code note: The IRC is a model code and local adoption/amendments control. AWC’s DCA 6 is based on the 2015 IRC and its prescriptive member tables are based primarily on 40 psf live load + 10 psf dead load. Do not treat DCA 6 as the current locally adopted code or as applicable to every deck configuration.
How Many Footings Do I Need for a Deck? Final Answer
The number of deck footings you need follows the structural post layout—not deck square footage alone.
Determine the beam lines first. Then determine the allowable span of each selected beam between posts. That establishes the primary post locations and, for a conventional post-and-footing foundation, the primary footing locations.
joists → beams → posts → footings → soil
Don’t start by counting footings. Design the framing first. The footing count follows.
Continue with the Deck Footing Spacing Guide, Deck Footing Size Chart, Deck Post Spacing Chart, and Deck Footing Calculator.
Related Deck Foundation & Framing Guides
Deck Framing Guide
Follow the complete structural load path from joists through the foundation.
Deck Footing Spacing Guide
Learn how beam span and post layout establish footing locations.
Deck Footing Size Chart
Size the bearing area after the support reactions and soil assumptions are established.
Deck Post Spacing Chart
See how allowable beam span controls the distance between structural posts.
Deck Tributary Area
Understand how deck area becomes a reaction at each post and footing.
How to Build a Freestanding Deck
See why independent beam lines change the support and foundation layout.