Concrete Footing Calculator
Calculate concrete volume and bag requirements for fence posts, deck footings, and pier foundations.
Formula & Explanation
A rectangular footing volume is calculated using: Volume (cu ft) = Length (ft) × Width (ft) × Depth (ft) All dimensions are entered in feet. To convert cubic feet to cubic yards, divide by 27. The number of bags depends on the concrete yield (typically 0.45 cu ft for 60 lb bags, 0.60 cu ft for 80 lb bags). A waste percentage (typically 10%) accounts for spillage and uneven ground. Final bags = ceil(Volume × (1 + Waste%) ÷ Bag Yield)
Assumptions
- •The footing is rectangular with uniform dimensions
- •All measurements are in feet
- •Bag yield values are industry standards-confirm with your product
- •Depth is the vertical distance below grade; frost line requirements vary by region
- •A 10% waste allowance is typical; adjust for site conditions
Example Calculation
A 4 ft × 4 ft footing dug 2 feet deep requires 32 cubic feet of concrete. With 10% waste and 60 lb bags (0.45 cu ft yield), you need 79 bags.
Inputs
Results
Standard Footing Sizes & Concrete Volume
| size | volume_cuft | volume_cuyd | bags_60lb |
|---|---|---|---|
| 2 × 2 ft, 2 ft deep | 8 | 0.30 | 20 |
| 3 × 3 ft, 2 ft deep | 18 | 0.67 | 45 |
| 4 × 4 ft, 2 ft deep | 32 | 1.19 | 79 |
| 4 × 4 ft, 3 ft deep | 48 | 1.78 | 119 |
| 6 × 6 ft, 3 ft deep | 108 | 4 | 268 |
Frequently Asked Questions
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