How much concrete for a 12×12 footing?
A 12 in × 12 in × 12 in footing is 1 cubic foot, or about 2 × 80 lb bags. A 12 in × 12 in footing 8 ft long is 8 cubic feet, or about 14 × 80 lb bags before waste.
Footing calculator
Concrete Footing Calculator
Estimate concrete for strip footings, pad footings, deck posts and columns. Enter length, width and height to get volume, bag counts and a cost estimate.
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How to calculate concrete for a footing
Footing volume = length × width × height. For multiple identical footings, calculate one and multiply by the number of footings. Divide cubic feet by 27 for cubic yards.
Example: 8 ft × 1 ft × 1 ft footing
8 × 1 × 1 = 8 cubic feet. Divide by 27 to get 0.30 cubic yards. Add 10% waste for about 0.33 cubic yards, or roughly 16 × 80 lb bags.
Common footing sizes
| Size | Concrete | 80 lb bags* |
|---|---|---|
| 12 in × 12 in × 12 in | 1.00 cu ft | 2 |
| 12 in × 12 in × 8 ft | 8.00 cu ft | 14 |
| 18 in × 18 in × 8 ft | 18.00 cu ft | 32 |
| 24 in × 24 in × 8 ft | 32.00 cu ft | 56 |
*Before waste. Add 5–10% for spillage and uneven subgrade.
Tips for ordering concrete for a footing
- Calculate one footing first, then multiply by the number of identical footings.
- Add 5–10% waste for over-excavation and uneven trench bottoms.
- Use the engineered footing size and depth; soil capacity and frost depth vary by location.
- Rebar is common in structural footings. Confirm the bar size, spacing and cover with your plan.
Concrete Footing Calculator FAQ
How many bags of concrete for deck footings?
It depends on the footing size and count. A 12 in × 12 in × 8 ft footing needs about 14 × 80 lb bags before waste. Measure each footing, calculate one, then multiply by the number of footings.
How deep should a concrete footing be?
Footing depth depends on the load, soil and local frost line. Deck and porch footings commonly extend below the frost line; follow the engineered plan or your local building code.
Do footings need rebar?
Structural footings often include rebar, but the requirement depends on the design. Use the bar size, spacing and cover shown on the engineered plan, or ask your inspector before pouring.
How do I calculate multiple footings?
Calculate the volume of one footing, multiply by the number of identical footings, then add a 5–10% waste allowance. The calculator handles one footing at a time.
How much does a concrete footing cost?
At $120–$180 per cubic yard, a 0.33 cubic yard footing costs about $40–$60 in ready-mix before delivery. Small jobs may have minimum loads or short-load fees, so bagged mix can be cheaper.
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