General
Concrete Calculator
Calculate cubic yards and bags of concrete needed for slabs, footings, and pours.
40 cubic feet ÷ 27 = 1.48 cubic yards. With 10% overage: 1.63 cubic yards. Order ready-mix concrete by the yard. Bag concrete is practical up to ~1 cubic yard - above that, ready-mix is more economical.
Common Questions
How do I calculate yards of concrete needed?
Multiply length times width times thickness in feet. Divide by 27 to convert cubic feet to cubic yards. Add 10 percent for waste. For a 10x10 foot slab at 4 inches thick, you need about 1.23 cubic yards.
How many bags of concrete equal one yard?
One cubic yard of concrete takes about 45 bags of 60 pound concrete mix or about 34 bags of 80 pound mix. Mixing by hand is practical only for small jobs under 1 yard.
When should I order ready-mix instead of mixing bags?
Order ready-mix concrete for anything over 1 cubic yard. It is cheaper per yard, comes out stronger and more consistent, and saves hours of mixing time on the job.
How thick should a concrete slab be for a patio or driveway?
A residential patio slab should be 4 inches thick. Driveways that carry passenger vehicles need 4 to 5 inches. Areas with heavy trucks or equipment need 6 inches or more with proper rebar.
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