Concrete Calculator
Enter the slab size and thickness to see how much concrete to order, in cubic yards for a truck or in bags for small pours.
Results are estimates for planning only. Always confirm measurements, local codes and manufacturer specs before ordering materials or quoting a job. See our Terms.
How to calculate concrete
Cubic yards = length (ft) x width (ft) x thickness (in) / 12 / 27. Ready-mix trucks sell by the cubic yard, usually with a minimum order, so small pours are often cheaper with bags.
An 80 lb bag makes about 0.6 cubic feet; a 60 lb bag about 0.45 cubic feet. Always order 5 to 10% extra for uneven ground and spillage.
Questions
How thick should a concrete slab be?
Patios and walkways are typically 4 inches. Driveways are usually 4 to 6 inches, and areas for heavy vehicles 6 inches or more.
How many bags of concrete make a yard?
About 45 bags of 80 lb concrete or 60 bags of 60 lb concrete make one cubic yard.
When should I order ready-mix instead of bags?
For anything over about 1 cubic yard, ready-mix delivery is usually faster and more consistent than mixing bags.