Concrete Footing Calculator
Estimate how much concrete you need for a continuous rectangular footing — in cubic yards and cubic meters — with an optional waste allowance for spillage and trench irregularity.
Result
| Volume | |
| Volume (metric) | |
| Order quantity (with waste) |
Units & conversions used
Imperial inputs are feet (length) and inches (width, depth); results are shown in cubic feet, cubic yards (1 yd³ = 27 ft³) and cubic meters (1 ft³ = 0.02832 m³). Metric inputs are converted first: 1 m = 3.28084 ft, 1 cm = 0.3937 in.
Formula & source
V(yd³) = V(ft³) ÷ 27
Source: basic rectangular-prism geometry — the standard formula for the volume of a box. The 5–10% waste allowance is standard ready-mix ordering practice (covers spillage, form deflection and trench unevenness); it is an industry rule of thumb, not a code requirement. Footing structural design (width, depth, reinforcement, frost depth) is governed by the building code (IRC / ACI 318) and soil conditions — this calculator does not cover that.
Worked example (you can verify by hand)
Input: 30 ft long × 16 in wide × 8 in deep, 5% waste.
- Width in feet: 16 ÷ 12 = 1.3333 ft; depth in feet: 8 ÷ 12 = 0.6667 ft
- Volume: 30 × 1.3333 × 0.6667 = 26.67 ft³
- Cubic yards: 26.67 ÷ 27 = 0.9877 yd³
- With 5% waste: 0.9877 × 1.05 = 1.0370 yd³
Expected output: 26.67 ft³ = 0.99 yd³ (1.04 yd³ with waste), 0.76 m³ (0.79 m³ with waste).
Limitations — what this cannot do
- This estimates volume only. It does not design the footing: width, depth, concrete strength and reinforcement follow the building code (IRC / ACI 318), frost depth and soil bearing capacity; consult a structural engineer for load-bearing footings.
- Assumes a perfectly rectangular footing of uniform cross-section. Stepped footings, pads, or bell-bottoms need to be broken into sections (or use our slab/column calculators for those parts).
- Trenches are rarely perfectly straight — a hand-dug trench may need a bit more than the calculated waste allowance.
FAQ
How many cubic yards of concrete do I need for a 30-foot footing that is 16 inches wide and 8 inches deep?
30 × (16 ÷ 12) × (8 ÷ 12) = 26.67 ft³ ÷ 27 = 0.99 yd³. Order about 1.04 yd³ with a 5% allowance. Most suppliers round up to the nearest quarter or half yard.
What is the formula for footing concrete volume?
Volume = length × width × depth, all in the same units. With length in feet and width/depth in inches: V(ft³) = L(ft) × W(in) ÷ 12 × D(in) ÷ 12, then divide by 27 for cubic yards.
Should I add extra for waste?
Yes — 5–10% is standard practice. Trench bottoms are uneven, forms can spread slightly, and some concrete sticks to the chute. Running short means a cold joint in a structural element, which is worse than leftover concrete.
How wide and deep should my footing be?
This calculator cannot answer that — it only estimates volume. Footing size depends on wall loads, soil bearing capacity and frost depth under your local building code. Check the approved plan or ask an engineer.