Concrete Footing Calculator
Calculate the concrete for footings from length, width, depth and count — in cubic yards and bags.
How it works
cubic feet = length(ft) × (width ÷ 12) × (depth ÷ 12) × count · cubic yards = cubic feet ÷ 27
A footing is a long prism: its length is in feet while the cross-section (width and depth) is in inches, so both of those are divided by 12. Multiply by the number of identical footings, then divide by 27 for cubic yards. Continuous wall footings use the full run length; isolated pier footings use their individual size with a count.
Worked example
A 20 ft footing 16 in wide and 8 in deep: 20 × (16 ÷ 12) × (8 ÷ 12) = 17.8 cu ft, ÷ 27 = 0.66 cubic yards — about 40 sixty-pound or 30 eighty-pound bags.
Frequently asked questions
How deep do footings need to be?
Below the local frost line, which ranges from a few inches in the South to 4 feet or more in the North. Frost heave under a shallow footing will crack whatever sits on it, so this is strictly a code question for your area.
Should footings be wider than the wall?
Yes — a footing spreads the load, so it is typically twice the wall width and at least as deep as the wall is thick. Your local code and the soil’s bearing capacity set the exact dimensions.
Do I need rebar in a footing?
Most codes require at least two continuous horizontal bars, and more where soils are weak or loads are high. Rebar does not change the concrete volume, but forgetting it can fail an inspection.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.