Concrete Footing Calculator
Enter the length, width and depth of your footing to get cubic yards and bags. Add each run of footing as its own area and the calculator totals them.
Last updated November 13, 2026
How to calculate concrete for a footing
A strip footing is a long rectangle: volume = length × width × depth. Width and depth are usually measured in inches, so divide each by 12 first.
Example: a 40 ft footing, 16 inches wide and 8 inches deep, is 40 × 1.333 × 0.667 = 35.6 cubic feet, or 1.32 cubic yards. With 10% for waste, order 1.5 yards.
Concrete per linear foot of footing
| Footing size (width × depth) | Cubic feet per foot | Cubic yards per 100 ft | 80 lb bags per 10 ft |
|---|---|---|---|
| 12 in × 6 in | 0.50 | 1.85 | 9 |
| 16 in × 8 in | 0.89 | 3.29 | 15 |
| 18 in × 8 in | 1.00 | 3.70 | 17 |
| 20 in × 10 in | 1.39 | 5.14 | 24 |
| 24 in × 12 in | 2.00 | 7.41 | 34 |
Multiply the first column by your total length. For a house footprint, add all four sides and any interior footings.
Why footing pours come up short
- Trench walls are not straight. An earth-formed trench is almost always wider than the drawing. Use 10% waste or more.
- Corners get counted twice or not at all. Measure along the centerline of the footing.
- Stepped footings on a slope need each step added as its own area.
- Pads under posts are separate pours. Add them as extra areas.
Footing size, depth below frost and reinforcement are set by your local code. This calculator only works out the quantity.
Concrete footer calculator for decks and posts
Footer and footing mean the same thing. For a deck or a post, the footing is usually a square or round pad rather than a long strip. For a square pad, multiply length × width × depth, all in feet.
| Pad footing | Cubic feet | 80 lb bags each |
|---|---|---|
| 12 × 12 × 12 in | 1.00 | 2 |
| 16 × 16 × 8 in | 1.19 | 2 |
| 24 × 24 × 12 in | 4.00 | 7 |
| 30 × 30 × 12 in | 6.25 | 11 |
Multiply by the number of footings, then add about 10%. Footing size and depth are set by the load and by your local frost depth, so take the dimensions from your plans or building department. For round piers poured in tube forms, use the sonotube calculator.
Frequently asked questions
How do I calculate concrete for a footing?
Multiply length × width × depth, all in feet, to get cubic feet. Divide by 27 for cubic yards. A 40 ft footing that is 16 inches wide and 8 inches deep is 40 × 1.333 × 0.667 = 35.6 cubic feet, or 1.32 cubic yards.
How much concrete is in a footing per foot?
A 16 inch × 8 inch footing holds 0.89 cubic feet per linear foot. A 24 inch × 12 inch footing holds 2 cubic feet per foot.
How wide and deep should a footing be?
That is set by your local building code and depends on the load, the soil and the frost depth. Check with your building department before you dig.
How do I calculate a round footing?
Use the post hole or sonotube calculator: 3.1416 × radius² × depth.
Is a footer the same as a footing?
Yes. Footer is the everyday word and footing is the term used in building codes. Both mean the concrete base that spreads a load into the ground.