This trapezoidal footing volume calculator finds the concrete volume of a sloped (frustum-shaped) footing from the top and bottom areas and the height. Enter the values above.
Formula (frustum)
V = h ÷ 3 × (Atop + Abottom + √(Atop × Abottom))
Example
Abottom = 4 m², Atop = 1 m², h = 0.5 m: V = 0.5/3 × (4 + 1 + 2) = 1.17 m³.
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Frequently Asked Questions
How do I calculate trapezoidal footing volume?
Use the frustum formula: height over 3, times the sum of the two areas plus the square root of their product.
Why is a footing trapezoidal?
The sloped sides use less concrete than a full block while still spreading the load to the soil.
What are the top and bottom areas?
The bottom is the base bearing on soil; the top is the smaller area under the column or pedestal.