Concrete Footing Calculator
Short answer: footing volume = length × width × depth ÷ 27 (cubic yards). Round column = π × radius² × height ÷ 27. Enter identical footings once and set the count to total them.
Calculate your footing
How footing math works
Rectangular footing: volume (cu ft) = length (ft) × width (ft) × depth (ft). A 40 ft strip, 2 ft wide, 1 ft deep = 80 cu ft = 2.96 cubic yards.
Round column: volume (cu ft) = π × (diameter ÷ 2)² × height. A 12-inch diameter pier, 4 ft tall = 3.14 cu ft = 0.12 cubic yards each.
Multiple pours: identical footings are calculated once and multiplied by the count. Different sizes must be calculated separately and added.
Common strip footings — per 10 ft run (net, before waste):
| Footing size | Cubic yards | 80 lb bags |
|---|---|---|
| 12 in wide × 12 in deep | 0.37 | 17 |
| 16 in wide × 12 in deep | 0.49 | 23 |
| 18 in wide × 12 in deep | 0.56 | 26 |
| 24 in wide × 12 in deep | 0.74 | 34 |
| 24 in wide × 18 in deep | 1.11 | 50 |
Bag counts use the 0.60 cu ft yield and are rounded up. For a longer run, multiply by length ÷ 10 — the 24 in × 12 in footing needs 2.96 cubic yards for a 40 ft run.
Frequently asked questions
How do you calculate concrete for a footing?
For a rectangular footing, multiply length × width × depth (all in feet) to get cubic feet, then divide by 27 for cubic yards. For a round column, use pi × radius squared × height. Add 5–10% waste, or 15–20% for hand-dug trenches.
How deep should a footing be?
Typically 12 to 48 inches depending on region and code, and usually below the frost line. Check your local code — depth is structural, not a calculator default.
Does this calculator include rebar for a footing?
No — it estimates concrete volume only. Reinforcement, footing width and depth are structural decisions; follow your local building code and, where required, an engineer's design.