Footing calculator
Sizes a continuous strip footing. Footing dimensions and depth are engineer-specified under ACI 318 and ACI 332, and the required depth below grade is set by your local building department — this tool computes volume for dimensions you already have, it does not size the footing.
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This calculator needs JavaScript. The reference table below covers the common cases.
| Footing size | ft³ per 10 ft | yd³ per 10 ft |
|---|---|---|
| 12 × 6 in | 5.0 | 0.19 |
| 16 × 8 in | 8.9 | 0.33 |
| 20 × 8 in | 11.1 | 0.41 |
| 24 × 12 in | 20.0 | 0.74 |
The formula
width (in ÷ 12) × depth (in ÷ 12) × length (ft) ÷ 27 = cubic yards
Worked example
A 16 in wide × 8 in deep footing running 60 ft: 1.333 × 0.667 × 60 = 53.3 ft³. 53.3 ÷ 27 = 1.98 yd³.
Reference table
| Footing size | ft³ per 10 ft | yd³ per 10 ft |
|---|---|---|
| 12 × 6 in | 5.0 | 0.19 |
| 16 × 8 in | 8.9 | 0.33 |
| 20 × 8 in | 11.1 | 0.41 |
| 24 × 12 in | 20.0 | 0.74 |
Assumptions
- Assumes a rectangular cross-section of constant dimensions.
- Does not add volume for keyways, steps, or over-excavation.
- Footing size and reinforcement are engineer-specified. Verify frost depth with your local building department.