Footing Sizing Estimator
Estimate the plan size of a square, rectangular or strip spread footing from the column load and allowable soil bearing pressure, accounting for footing and backfill self-weight.
Input
Unfactored dead + live load delivered to the footing.
Depth from ground surface to the underside of the footing.
Output
| Property | Value |
|---|---|
| No data yet | |
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/footing-sizing-estimator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"load": "800",
"bearing": "200",
"type": "square"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `footing-sizing-estimator` tool (Footing Sizing Estimator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.
Embed widget
<iframe
src="https://iotools.cloud/embed/footing-sizing-estimator/"
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title="Footing Sizing Estimator — iotools.cloud"
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| Cost per API/MCP call | From 5 credits |
|---|---|
| Need more credits? | View pricing |
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Guides
A spread footing must be big enough that the soil pressure under it stays below the allowable bearing pressure. This estimator takes the service load and soil capacity, deducts the weight of the footing and the soil above it, and returns the plan size needed.
The formulas
overburden = 24 × t + γs × (Df − t) (kPa)
qnet = qa − overburden
A = P / qnet
B (square) = √A B (rectangular) = √(A / ratio), L = ratio × B
strip width = P / qnet (per metre of wall)t is the footing thickness, Df the founding depth, γs the soil unit weight and 24 kN/m³ the weight of concrete. Suggested sizes are rounded up to the next 50 mm, and the pressure is rechecked at that size.
Worked example: an 800 kN column on 200 kPa soil with Df = 1 m and t = 0.5 m. Overburden is 12 + 9 = 21 kPa, qnet = 179 kPa, area = 4.47 m², so a 2.11 m square — suggested 2.15 × 2.15 m.
How to use it
- Enter the unfactored service load and the allowable bearing pressure.
- Pick square, rectangular or strip footing (and a ratio for rectangular).
- Optionally set founding depth, thickness and soil unit weight.
FAQ
Should I use factored or service load? Service (unfactored) load, because allowable bearing pressure is a working-stress value.
What does this not cover? Footing thickness for punching and beam shear, reinforcement, moments or eccentric loads, settlement and groundwater. Treat it as a first sizing step.