About the concrete calculator
Pick the shape you are pouring, enter its size and the calculator finds the volume of concrete in cubic yards (US) or cubic meters (metric). It supports flat slabs, round columns or piers, and solid stairs where every step is poured on top of the ones below.
A waste allowance covers spillage, uneven ground and over-excavation. The result also converts the volume into the number of premixed bags of the size you choose, rounded up, and estimates the cost when you enter a price.
Ordering tips
Bag yields are approximate: a 60 lb bag makes about 0.45 cubic feet and an 80 lb bag about 0.6 cubic feet. For large pours, ready-mix delivery by the cubic yard is usually cheaper than bags.
Formula
- Slab: volume = length × width × thickness
- Column: volume = π × (diameter ÷ 2)² × height × count
- Stairs: volume = run × rise × width × n(n + 1) ÷ 2
- Order = volume × (1 + waste ÷ 100); 1 yd³ = 27 ft³
Example
A 10 ft by 10 ft slab 4 inches thick is 33.33 ft³, or 1.23 yd³. With 10% waste you need 1.36 yd³, about 82 bags of 60 lb.