Concrete Calculator
Enter the dimensions of your slab, footing, or column to find out exactly how much concrete you need — in cubic yards and in bags.
Concrete needed
How the concrete calculator works
Concrete is sold by the cubic yard (one cubic yard = 27 cubic feet). To estimate your project, we multiply length × width × thickness to get the volume in cubic feet, divide by 27 to convert to cubic yards, then add a waste allowance for spillage and uneven sub-base.
Bag counts assume each 80 lb bag yields about 0.60 cubic feet and each 60 lb bag yields about 0.45 cubic feet of mixed concrete. For anything larger than about 1 cubic yard, ready-mix delivery is usually cheaper than bags.
- Slabs & patios: 4 inches is standard; use 5–6 inches for driveways.
- Footings: check your local code for required depth and width.
- Always round up — running short mid-pour is far worse than a little extra.
Frequently asked questions
How many 80 lb bags are in a cubic yard?
About 45 bags of 80 lb concrete mix make one cubic yard. That's why bagged concrete only makes sense for small jobs — bigger pours are cheaper with ready-mix delivery.
How thick should a concrete slab be?
4 inches is typical for patios and walkways. For driveways or anything carrying vehicle weight, go with 5–6 inches and consider rebar or wire mesh.
Why add a waste allowance?
Forms are rarely perfect, the ground isn't perfectly level, and some concrete is always lost to spillage. A 10% buffer keeps you from coming up short.