Concrete Footing Calculator
Footings transfer structural loads into the ground — getting the concrete volume right before you pour is critical. This calculator handles rectangular strip footings (for walls and fences) and pad footings (for posts and columns). Enter your dimensions to get cubic yards, waste-adjusted volume, and bag count for smaller pours.
How to use this calculator
- Enter the footing width and depth in inches.
- Enter the total length of the footing run in feet.
- Adjust the waste factor for your site conditions.
- Read your cubic yards — footings under 1 yd³ can often use bagged mix.
How we calculate this
Footing volume = width × depth × length, converted to cubic yards (÷ 27). A 12-inch wide by 12-inch deep footing running 20 linear feet is 1 × 1 × 20 = 20 cubic feet = 0.74 cubic yards. We add 10% waste for form blowout, uneven trench bottoms, and spillage. Most residential footings are under 2 yards — bags are common, but ready-mix is faster for larger foundations.
What this calculator doesn't include
This calculator covers concrete volume only. Footing dimensions should be specified by a structural engineer or your local building code — minimum footing sizes vary by soil bearing capacity, frost depth, and load. This calculator does not account for rebar (always required in footings), form materials, or excavation.
Example concrete estimates — Concrete Footing
Pre-calculated for common project sizes. Includes 10% waste factor.
| Dimensions | Cubic Yards | With Waste | 80 lb Bags |
|---|---|---|---|
| 12" W × 12" D × 10 ft L | 0.37 yd³ | 0.41 yd³ | 19 |
| 12" W × 12" D × 20 ft L | 0.741 yd³ | 0.82 yd³ | 37 |
| 16" W × 8" D × 10 ft L | 0.329 yd³ | 0.36 yd³ | 17 |
| 16" W × 8" D × 20 ft L | 0.658 yd³ | 0.72 yd³ | 33 |
| 24" W × 12" D × 10 ft L | 0.741 yd³ | 0.82 yd³ | 37 |
| 24" W × 12" D × 20 ft L | 1.481 yd³ | 1.63 yd³ | 74 |
| 36" W × 12" D × 10 ft L | 1.111 yd³ | 1.22 yd³ | 55 |
| 36" W × 12" D × 20 ft L | 2.222 yd³ | 2.44 yd³ | 110 |
All estimates include a 10% waste factor. Under 1 yd³ is typically practical with bagged mix; over 1 yd³ usually warrants a ready-mix truck.
Frequently asked questions
Minimum footing dimensions depend on local building code and soil bearing capacity. A common rule of thumb: the footing should be at least as wide as the wall it supports, and at least 12 inches deep below the frost line. In cold climates, frost depth can be 3–4 feet. Always check your local code before designing footings.
A strip footing (also called a continuous footing) runs under a wall or fence line — it is long, relatively narrow, and distributes load along its length. A pad footing (also called a spread footing) is a square or rectangular block under an individual column or post. This calculator handles both — strip footings use length, pad footings use a short length equal to the pad dimension.
Yes, in virtually all structural applications. Concrete is strong in compression but weak in tension — rebar handles the tensile forces. Most building codes require a minimum of two horizontal rebar runs in a footing, tied at corners. Consult your local code and a structural engineer for specific requirements.
Concrete reaches approximately 70% of its design strength in 7 days and full strength (28-day strength) in about 28 days. For light loads like fence posts, you can typically backfill and proceed after 24–48 hours of curing. For structural loads like walls and columns, wait at least 7 days and ideally the full 28 days.
Yes for smaller footings — post bases, fence posts, and small pad footings under 1 cubic yard. Fast-setting bag mixes (like Quikrete Fast Setting) can be poured dry into the hole and watered in place, reaching working strength in 20–40 minutes. For strip footings over 1 yard, ready-mix is faster, cheaper per unit, and gives a more consistent result.