BuildCalc

Concrete Footing Calculator

Estimate concrete for round footings, piers, sonotubes and post holes. Enter the tube diameter, the depth of each hole and how many you are pouring — the calculator returns the total cubic yards and how many bags of concrete you need.

Concrete for footings
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    How it works

    Each round footing holds π × radius² × depth of concrete, where radius = (diameter ÷ 12) ÷ 2 in feet. Total volume = per-footing volume × number of footings, plus waste. 80 lb bags = cu ft ÷ 0.60, rounded up.

    Frequently asked questions

    How much concrete does a sonotube hold?

    A 12 in tube holds about 0.79 cu ft per foot of depth; an 8 in tube about 0.35 cu ft/ft; a 10 in tube about 0.55 cu ft/ft. Multiply by depth and the number of tubes.

    How many bags of concrete per post hole?

    A 12 in wide hole 3 ft deep is roughly 2.4 cu ft, or about 4 bags of 80 lb. Deeper or wider holes climb fast, which is why this calculator lets you set diameter, depth and count.

    How deep should a footing be?

    Deck and fence footings usually go below the frost line — often 36–48 in in cold climates — and rest on undisturbed soil. Always follow local code.

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    Estimates are for planning only. Material yields, densities and code requirements vary — confirm quantities with your supplier and local building code before ordering.