How the number is worked out
strip = length (ft) × width (in) ÷ 12 × depth (in) ÷ 12
square pad = (width ÷ 12)² × depth ÷ 12, times the number of pads
For a strip that runs around a rectangle, measure the length along the centre line of the trench. Adding the four outside edges counts each corner twice.
Worked examples
Strip: 40 ft long, 16 in wide, 8 in deep. 40 × 16 ÷ 12 × 8 ÷ 12 = 35.56 ft³ (1.32 yd³) → 35.56 ÷ 0.60 = 59.3 → 60 bags of 80 lb.
Pads: four pads, 24 in square, 12 in deep. 2 × 2 × 1 = 4 ft³ each, 16 ft³ in all → 27 bags of 80 lb shared, or 7 × 4 = 28 if each pad gets whole bags.
What this calculator is not for
Footing width and depth are set by the load, the soil and your local code and frost depth. This page only turns the sizes you already have into a quantity of concrete. It does not account for rebar, stepped footings or trenches with sloping sides.
Sources
- QUIKRETE, QUIKRETE® Concrete Mix (No. 1101) — Product Data Sheet. Checked 2026-09-24.
- QUIKRETE, QUIKRETE® 5000 High Early Strength Concrete Mix (No. 1007) — Product Data Sheet. Checked 2026-09-24.
- QUIKRETE, QUIKRETE® Fast-Setting Concrete Mix (No. 1004) — Product Data Sheet (revised November 2025). Checked 2026-09-24.
- Sakrete, Sakrete 5000 Plus High Early Strength Concrete Mix — Technical Data Sheet. Checked 2026-09-24.
- Sakrete, Sakrete Fast Setting Concrete Mix — Technical Data Sheet. Checked 2026-09-24.
- QUIKRETE, QUIKRETE® Quantity Calculator. Checked 2026-09-24.
- Sakrete, Sakrete Calculators. Checked 2026-09-24.
- NIST, NIST Handbook 44 (2026), Appendix C — General Tables of Units of Measurement. Checked 2026-09-24.
“1 728 cubic inches (in3) = 1 cubic foot (ft3) 27 cubic feet = 1 cubic yard (yd3)”