Concrete Calculator

How the concrete calculation works

Concrete is sold by volume. Multiply length × width × depth — with depth converted from inches to feet (inches ÷ 12) — to get cubic feet, then divide by 27 to get cubic yards, the unit ready-mix trucks use. For bagged pre-mix, each bag yields a fixed volume once mixed: an 80 lb bag makes about 0.60 cubic feet, a 60 lb bag about 0.45 cubic feet, and a 50 lb bag about 0.375 cubic feet. The bag counts above divide your total volume by those yields and round up — you can't buy a partial bag.

Always add a waste allowance of 5–10%. Subgrade is never perfectly level, forms bow slightly, and some concrete stays in the wheelbarrow or spills. Running short mid-pour means a cold joint and a weak slab; a standard 10% cushion is cheap insurance. If you're ordering ready-mix, tell the dispatcher your exact calculation and the waste percentage — most suppliers suggest rounding the order up to the nearest quarter yard, and many charge a short-load fee for orders under 4–5 yards, which is why small jobs are often cheaper by the bag.