How to calculate footing concrete
Volume = total footing length × width × depth. Measure the length along the centreline of the walls: the perimeter of the house plus any interior bearing walls. For pad footings under posts, set the quantity.
Worked example
100 ft × 2 ft × 1 ft = 200 ft³, which is 200 ÷ 27 = 7.4 yd³. With 5% waste, order about 7.8 yd³, or 8 yd³ from the plant.
Typical footing sizes
For a one- or two-storey house on good soil, strip footings are often 16–24 in wide and 8–12 in thick, with the bottom below the local frost line. Your local code and the soil conditions decide the final size.
Frequently asked questions
How many yards of concrete for a 24 x 24 garage footing?
The perimeter is 96 ft. At 16 in × 10 in that is 96 × 1.33 × 0.83 = 107 ft³, about 4 yd³ plus waste.
How deep should a footing be?
Below the frost line for your area and on undisturbed soil; the footing thickness itself is usually 8–12 in.