Deck Footing Calculator
Estimate footing bearing area and concrete volume from load and soil capacity.
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What this tool does
Estimate footing bearing area and concrete volume from load and soil capacity. Equal tributary loads are assumed. Frost depth, uplift and reinforced footing design are not checked.
How to use the Deck Footing Calculator
- Enter or select total tributary load.
- Enter or select allowable soil bearing (lb/sq ft).
- Enter or select number of equal-loaded footings.
- Enter or select concrete depth in in.
- Read the calculated result; change any measurement to compare alternatives.
Formula
area per footing = load / count / soil; circular diameter = sqrt(4×area/π); volume = count × area × depth/12
- load
- Total tributary load
- soil
- Allowable soil bearing (lb/sq ft)
- count
- Number of equal-loaded footings
- depth
- Concrete depth (in, before metric conversion)
Equal tributary loads are assumed. Frost depth, uplift and reinforced footing design are not checked.
Worked example
For deck footing calculator, the following measurements illustrate the exact method: Total tributary load: 6000; Allowable soil bearing (lb/sq ft): 1500; Number of equal-loaded footings: 4; Concrete depth: 12.
Inputs
- Total tributary load6000
- Allowable soil bearing (lb/sq ft)1500
- Number of equal-loaded footings4
- Concrete depth12 in
Result
- Required circular diameter13.54 in
- Bearing area per footing1 sq ft
- Concrete volume0.15 cu yd
Results explained
- Required circular diameter
- Required circular diameter from the formula above, expressed in in before metric conversion. Equal tributary loads are assumed. Frost depth, uplift and reinforced footing design are not checked.
- Bearing area per footing
- Bearing area per footing from the formula above, expressed in sqft before metric conversion. Equal tributary loads are assumed. Frost depth, uplift and reinforced footing design are not checked.
- Concrete volume
- Concrete volume from the formula above, expressed in yd3 before metric conversion. Equal tributary loads are assumed. Frost depth, uplift and reinforced footing design are not checked.
Frequently asked questions
Divide the tributary load by allowable bearing pressure and number of footings.
Use professionally established soil capacity and actual tributary loads.
Round dimensions up, but have the whole footing design checked.
Split the outline into rectangles or triangles and calculate each section separately. Do not count overlapping sections twice.
Local frost depth and structural design requirements still apply.