SteelSolver.com

Deck Footing Calculator

Calculate footing size, depth, concrete volume & IRC code compliance for deck piers — free, instant, no sign-up.

Deck Geometry

e.g. 16 ft (typical backyard deck)
e.g. 12 ft
Ledger to beam distance
Beam overhang past last post
Affects wind uplift check

Framing Layout

For attached decks, ledger is row 0
Typical: 6–10 ft
= joist span for single-beam attached
Auto-calculated; override if needed

Design Loads

IRC default: 40 psf residential
Typical: 10–15 psf
0 if no snow region. Overrides live load.
Hot tub, outdoor kitchen, planters
1.5
Typical: 1.5–2.0 for residential

Soil & Site Conditions

IRC/DCA-6 default tables use 1,500 psf
From soil type above or geotechnical report
In. — varies by region (0–60+). Add 6 in. buffer.
IRC minimum: 12 in. typically
Check ASCE 7 wind map for your zone
4–6 in. compacted crushed stone recommended

Footing Configuration

Bell footing resists frost heave uplift
10%
10% typical; 15% for complex pours

Calculation Results

Required Footing Diameter
—
inches
Recommended Tube Size
—
standard sonotube
Square Footing Side
—
inches
Required Footing Depth
—
inches
Tributary Area / Footing
—
sq ft
Total Load / Footing
—
lbs
Bearing Pressure
—
psf actual
Number of Footings
—
footings total

Code Compliance Checks

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—
—
—
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Concrete & Materials

ItemPer FootingTotal
Concrete Volume——
Concrete Volume (cu yd)——
60 lb Bags Required——
Gravel Base Volume——
Excavation Volume——
Estimated Cost (bags)——

ⓘ Includes 10% waste factor. Concrete bag yield: 40 lb=0.30 cu ft, 60 lb=0.45 cu ft, 80 lb=0.60 cu ft. Cost estimate based on $4–$6/bag.

IRC R507.3.1 Footing Size Reference

Minimum round footing diameter (inches) for soil bearing capacities per AWC DCA-6. Your calculated case is highlighted.

Tributary Area (sq ft) 1,500 psf 2,000 psf 2,500 psf 3,000 psf

Top-Down Deck Layout

Live diagram showing footing positions, beam lines, tributary areas, and dimensions. Updates with inputs.

Footing Cross-Section

Tributary Area

The tributary area is the deck area each footing must support. Interior footings carry the most load.

Interior Post / Footing
\[A_{trib} = \frac{S_{joist}}{2} \times S_{post}\]

where \(S_{joist}\) = joist span (ft), \(S_{post}\) = post spacing (ft)

Edge / Corner Footings (adjusted)
\[A_{trib,edge} = \frac{S_{joist}}{2} \times \frac{S_{post}}{2}\]

Design Load per Footing

Total Design Load
\[w_{design} = w_{dead} + \max(w_{live},\; w_{snow})\] \[P_{footing} = w_{design} \times A_{trib} + P_{point}\]

\(w_{dead}\) = dead load (psf), \(w_{live}\) = live load (psf), \(w_{snow}\) = ground snow load (psf)
\(P_{point}\) = additional point load (lbs, concentrated loads like hot tubs)

Required Footing Area & Size

Required Bearing Area
\[A_{req} = \frac{P_{footing}}{q_{allow} / SF}\]

\(q_{allow}\) = allowable soil bearing capacity (psf)
\(SF\) = safety factor (typically 1.5–2.0)

Round Footing Diameter
\[D = \sqrt{\frac{4 \cdot A_{req}}{\pi}}\]

Result rounded up to nearest inch, then to nearest standard sonotube size (8", 10", 12", 14", 16", 18", 20", 24")

Square Footing Side Length
\[L = \sqrt{A_{req}}\]

Concrete Volume

Round (Cylindrical) Footing
\[V_{concrete} = \pi \left(\frac{D}{2}\right)^2 \times d_{footing}\]

\(D\) = footing diameter (ft), \(d_{footing}\) = footing depth (ft)
Convert in → ft: divide by 12

Square Footing
\[V_{concrete} = L^2 \times d_{footing}\]
Total with Waste
\[V_{total} = V_{concrete} \times N_{footings} \times (1 + f_{waste})\] \[\text{Bags} = \left\lceil \frac{V_{total}}{V_{bag}} \right\rceil\]

\(f_{waste}\) = waste factor (e.g. 0.10 = 10%), \(V_{bag}\) = yield per bag (cu ft)

Required Footing Depth

Frost-Protected Depth
\[d_{req} = \max\left(d_{frost} + 6\text{ in},\; d_{code,\min}\right)\]

\(d_{frost}\) = local frost line depth (in)
Add 6 in. buffer below frost line per best practice (IRC R403.1.4.1)

Bearing Pressure & Utilization

Actual Bearing Pressure
\[q_{actual} = \frac{P_{footing}}{A_{provided}}\]
Utilization Ratio
\[U = \frac{q_{actual}}{q_{allow}} \times 100\%\]

PASS if U ≤ 100%, WARNING if U = 80–100%, FAIL if U > 100%

Uplift Resistance (Wind)

Approximate Footing Self-Weight
\[W_{footing} = V_{concrete} \times 150 \text{ pcf}\] \[\text{Uplift OK if } W_{footing} \geq F_{uplift}\]

Simplified check — consult ASCE 7 for engineered wind uplift in high-wind zones.

Printable / Permit Report

Generate a formatted summary of all inputs, calculations, and results suitable for permit submission or contractor reference.


    

  


  

    ⚠ Engineering Disclaimer: This calculator is provided for preliminary planning and estimation purposes only. Results are based on simplified engineering assumptions and IRC/DCA-6 prescriptive tables. This tool is not a substitute for stamped engineering drawings or a licensed structural engineer. Always verify all footing sizes, depths, and designs with your local building department and inspector before construction. Local codes, soil conditions, frost depths, and site-specific factors may require modifications. SteelSolver.com assumes no liability for construction decisions made based on these results.