Concrete Calculator
Estimate the concrete for a slab, patio, or footing — in cubic yards and in bags. Includes a 10% waste allowance.
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How it works
Multiply the slab dimensions in feet to get cubic feet, add 10% for waste and spillage, then divide by 27 for cubic yards. Bag counts use standard yields: an 80 lb bag makes about 0.60 ft³, 60 lb about 0.45 ft³, and 40 lb about 0.30 ft³.
Formula
Cubic yards = (L ft × W ft × Thickness ft × 1.10 waste) ÷ 27
Frequently asked questions
How many 80 lb bags of concrete make a yard?
About 45 bags of 80 lb concrete make one cubic yard, since each 80 lb bag yields roughly 0.60 cubic feet and a yard is 27 cubic feet.
How much concrete do I need for a 10x10 slab?
A 10 × 10 slab at 4 inches thick needs about 1.23 cubic yards (or roughly 60 bags of 80 lb mix) after a 10% waste allowance.
Should I order bags or ready-mix?
Bags are convenient for small jobs under about a cubic yard. For larger pours, ready-mix delivery is faster and usually cheaper.