How to Calculate Concrete for Footings
Treating a footing as its own rectangular (or stepped) volume
A simple strip footing
A continuous strip footing of uniform width and depth is calculated exactly like a slab: length × width × depth, in consistent units, converted to cubic yards or cubic metres at the end.
Stepped and T-shaped footings
Many footings combine a wider base (the footing) with a narrower stem wall or thickened edge above it — a T-shape in cross-section. Calculate each section as its own rectangular volume and add them together: the wide base footing, plus the narrower stem wall, each with its own width and depth.
Don't forget the reinforcement
Footings are almost always reinforced with rebar. Rebar quantity is a separate calculation from concrete volume — it depends on the spacing and number of bars specified by the design, not on the concrete volume itself. Calculate the two independently.
Worked Example
A T-shaped footing: a 24 in wide × 12 in deep base, plus a 12 in wide × 24 in tall stem wall, for a 40 ft run.
Base: 40 ft × (24/12) ft × (12/12) ft = 80 ft³
Stem: 40 ft × (12/12) ft × (24/12) ft = 80 ft³
Total: 160 ft³ = 5.93 yd³
Related Calculators
Related Guides
Sources
NIST SP 811
Unit conversion reference (cubic feet, cubic yards, cubic metres).
NIST SP 811 — reference