Typical residential deck footing sizes include:

• Small decks: commonly 12-inch footings
• Moderate residential decks: commonly 16-inch footings
• Larger decks: commonly 18–24-inch footings

Actual footing size depends on:

• tributary load
• beam span
• joist span
• post spacing
• soil bearing capacity
• snow load
• local code requirements

The following chart provides approximate residential planning ranges for common deck layouts under typical loading conditions.

Deck footings support the entire structural load of the deck, including:

• framing lumber
• decking boards
• railings
• furniture
• people using the deck
• snow loads in colder climates

If the soil beneath the footing cannot safely support the load, the footing may settle or shift.

Larger footings spread weight across more soil surface area, reducing pressure on the ground.

Deck framing follows a structural load path:

Every structural component transfers weight downward through the framing system.

Understanding this load path explains why footing size affects the stability of the entire deck structure.

Related: Deck Beam Span Chart, Deck Joist Span Chart, and Deck Post Spacing Chart.

Several structural variables determine how large deck footings must be.

Posts that are spaced farther apart carry more structural load from the beams above them.

Wider post spacing increases the tributary area supported by each footing.

As tributary load increases:

• beam loads increase
• post loads increase
• footings usually must become larger

Related: Deck Post Spacing Chart.

Longer beam spans and longer joist spans both increase structural load on the footing system.

Long joists transfer more load into the beam, and larger beam spans transfer more load into the posts and footings below.

General structural relationships:

• longer joists → heavier beam loads
• larger beam spans → larger footing loads
• wider post spacing → larger footing requirements

Related: Deck Joist Span Chart and Deck Joist Spacing.

Tributary load refers to the portion of the deck supported by a particular structural component.

Each footing supports part of the deck surface area through the posts and beams above it.

Larger tributary areas create larger structural loads.

Soil bearing capacity describes how much weight the soil can safely support.

Strong dense soils can support higher loads than weak or loose soils.

Weak soils require larger footings to distribute structural loads safely.

In climates where frost occurs, deck footings must extend below the frost line to prevent frost heave.

Frost heave occurs when freezing soil expands and pushes shallow footings upward.

Proper footing depth helps prevent:

• deck movement
• shifting posts
• uneven framing
• structural instability

Structural engineers often estimate footing size using a basic bearing-pressure formula:

Residential decks are commonly designed around approximately:

• 40 psf live load
• 10 psf dead load

Together, this equals roughly:

Imagine a footing supporting approximately 80 square feet of deck area.

Step 1 — Calculate total load:

Step 2 — Estimate soil bearing capacity:

Many residential planning assumptions use approximately:

Step 3 — Calculate required footing area:

Step 4 — Convert to round footing diameter:

Approximately 2.7 square feet corresponds to roughly:

This example illustrates why larger decks and wider post spacing often require significantly larger footings.

Many simplified online footing charts show footing size based only on post spacing or post size.

In reality, footing size depends on:

• tributary load
• beam span
• joist span
• soil bearing capacity
• snow load
• deck configuration

Some deck features dramatically increase structural loading and may require engineered footing design.

Examples include:

• hot tubs
• outdoor kitchens
• masonry fireplaces
• multi-level decks
• rooftop decks
• large snow loads

These features can increase tributary loads significantly beyond standard residential assumptions.

Concrete quantity depends on footing diameter and footing depth.

Example:

A 12-inch diameter footing approximately 3 feet deep requires roughly:

Concrete is usually estimated using:

• cubic feet
• cubic yards
• bag count calculators

Most residential decks use poured concrete footings installed below frost depth.

Typical footing installation includes:

• excavation
• cylindrical footing forms
• concrete placement
• post anchors

Alternative systems may include:

• helical screw piles
• precast footing systems
• engineered footing pads

Helical piles are often used where:

• excavation is difficult
• soil conditions are poor
• access is limited

Accurate footing layout and proper foundation construction are critical to long-term deck stability. These tools and materials are commonly used by contractors and DIY builders when planning footing locations, establishing elevations, and constructing deck foundations.

• Bosch Blaze Laser Distance Measure
  Useful for measuring footing locations, post spacing, beam runs, and overall deck dimensions accurately.
  
  View Bosch Blaze Laser Measure →


• Construction Master Pro Calculator
  Helps simplify deck framing calculations, footing sizing estimates, beam spans, stair layouts, and material planning.
  
  View Construction Master Pro →


• Quikrete Concrete Tube Forms (Sonotube)
  Commonly used to create round deck footings and maintain consistent footing dimensions during concrete placement.
  
  View Concrete Tube Forms →


• Simpson Strong-Tie Adjustable Post Bases
  Designed to connect deck posts securely to concrete footings while improving durability and moisture separation.
  
  View Simpson Post Bases →


• DEWALT DW088LG Green Cross Line Laser
  Projects bright green horizontal and vertical reference lines to help establish footing locations, align posts, verify beam elevations, and improve deck layout accuracy.
  
  View DEWALT DW088LG Green Cross Line Laser →

Disclosure: As an Amazon Associate, The Backyard Standard may earn from qualifying purchases at no additional cost to you.

• footings that are too small
• footings installed above frost depth
• poor soil preparation
• posts not centered on footings
• ignoring tributary load increases
• using generic charts without code verification

• deck settlement
• sloping or uneven deck surfaces
• beam sagging
• movement near posts
• cracking concrete
• shifting after freeze-thaw cycles

Larger footings increase:

• excavation work
• concrete volume
• labor time

However, undersized footings can create expensive structural repairs later.

How big should deck footings be?

Most residential deck footings commonly range from approximately 12–24 inches in diameter depending on tributary load and soil conditions.

Do deck footings need to go below the frost line?

Yes. In climates with freezing conditions, footings should extend below frost depth to prevent frost heave.

How far apart should deck footings be?

Most residential decks commonly use posts spaced around 6–10 feet apart depending on beam size and structural loading.

Can deck blocks replace concrete footings?

Deck blocks may work for some small ground-level decks, but most permanent decks require proper footings installed below frost depth.

Does soil type affect footing size?

Yes. Weak soils require larger footings because they support less pressure safely.

Do hot tubs require larger footings?

Yes. Hot tubs create very large concentrated loads that often require engineered footing design.

Why are some footing charts inaccurate?

Many charts ignore tributary load, soil conditions, beam span, and snow load — all of which affect actual footing requirements.

Deck footing size is one of the most important structural decisions in deck construction because every load from the deck ultimately transfers into the footing system.

While many residential decks use common footing sizes such as 12-inch, 16-inch, or 20-inch diameters, actual footing requirements depend on:

• tributary load
• beam span
• joist span
• post spacing
• soil strength
• frost depth
• local code requirements

Last reviewed: May 2026

• American Wood Council
• International Code Council
• North American Deck and Railing Association