Concrete for strip footings, per 10 ft
| Width × depth | cu ft | yd³ | 80 lb bags |
|---|---|---|---|
| 12 × 6 in | 5.00 | 0.19 | 9 |
| 16 × 8 in | 8.89 | 0.33 | 15 |
| 20 × 10 in | 13.89 | 0.51 | 24 |
| 24 × 12 in | 20.00 | 0.74 | 34 |
Concrete for square footing pads
| Pad size | cu ft | 80 lb bags |
|---|---|---|
| 12 × 12 × 8 in | 0.67 | 2 |
| 16 × 16 × 8 in | 1.19 | 2 |
| 18 × 18 × 10 in | 1.88 | 4 |
| 24 × 24 × 12 in | 4.00 | 7 |
| 30 × 30 × 12 in | 6.25 | 11 |
How to calculate a footing
For a footing that wraps around a building, measure along the center of the footing on every side and add them up, so the corners aren't counted twice.
Footing size basics
Home footings are often 16 to 24 inches wide and 8 to 12 inches deep, with the bottom below the frost line. The right size depends on the load and your soil, so check your local building code or permit drawings before you dig.
Common questions
How much concrete do I need for a footing?
Multiply length by width by depth, all in feet, then divide by 27 for cubic yards. A 40 ft long footing that is 16 in wide and 8 in deep needs about 1.32 cubic yards.
How deep should a concrete footing be?
Deep enough to sit below the frost line and on firm soil. In mild climates that can be 12 in; in cold climates it can be 4 ft or more. Your local building department sets the requirement.
How many bags of concrete for a 24×24 footing?
A 24 × 24 in pad that is 12 in deep holds 4 cubic feet, so about 7 bags of 80 lb.