Concrete guide
How Much Concrete Do I Need?
The amount of concrete you need depends on the length, width, and thickness of your project. For most slabs, you calculate volume first, then convert that volume into cubic yards.
Multiply length by width by thickness. If using feet and inches, convert thickness into feet first. Then divide cubic feet by 27 to get cubic yards.
Use the Concrete Calculator →Concrete Formula
Thickness must be in feet before using this formula. For example, 4 inches is 0.333 feet.
Common Concrete Slab Estimates
| Slab Size | Thickness | Concrete Needed |
|---|---|---|
| 10 × 10 ft | 4 in | 1.23 yd³ |
| 12 × 12 ft | 4 in | 1.78 yd³ |
| 20 × 20 ft | 4 in | 4.94 yd³ |
| 24 × 24 ft | 4 in | 7.11 yd³ |
Example
A 20 ft by 12 ft slab at 4 inches thick is 80 cubic feet. Divide 80 by 27 and you get about 2.96 cubic yards. With 10% waste, you should plan for about 3.26 cubic yards.
Should You Add Extra?
Yes. Most concrete projects should include 5–10% extra material to account for uneven ground, spillage, measurement differences, and ordering safety.