Footing Reinforcement Calculator
Estimate the design moment at the column face and the required bending reinforcement for a reinforced-concrete pad footing, worked per metre width.
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Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the net upward bearing pressure q in kPa (soil pressure less self-weight, factored to ultimate).
- Enter the footing width B and the column width c in metres; the tool finds the cantilever projection (B - c)/2.
- Enter the effective depth d in millimetres and, optionally, the steel yield fy to read the face moment and required steel area.
How it works
The pad is treated as a cantilever projecting from the column face. The projection is l = (B - c)/2, the moment at the face is M = q * l^2 / 2, and required steel uses the simplified lever arm z = 0.85 * d, giving As = M*1e6 / (0.85 * fy * z) in mm2/m.
Worked example
Worked example. For q = 150 kPa, B = 2.0 m, c = 0.4 m, d = 400 mm and fy = 500 MPa: l = (2.0 - 0.4)/2 = 0.8 m, M = 150 * 0.8^2 / 2 = 48 kNm/m and As = 48e6 / (0.85 * 500 * 340) = 332.18 mm2/m.
Common mistakes
- Using gross soil pressure instead of the net upward pressure acting on the footing.
- Skipping the shear checks; footings are very often governed by one-way or punching shear rather than bending.
- Entering c greater than or equal to B, which gives no cantilever and no design moment.
Frequently asked questions
Does this size the footing for shear?
No. It only covers bending steel. You must separately check one-way (beam) shear, two-way (punching) shear, development length and minimum steel.
What pressure should I enter?
Enter the net factored upward bearing pressure the soil applies to the footing, not the gross geotechnical bearing capacity.
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Tip: Enter any known values to calculate the remaining results.
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