How much concrete do I need?
Pick your shape, enter the size, and the calculator returns cubic yards for a ready-mix order and the number of 80 lb, 60 lb or 40 lb bags for a DIY mix. It adds a waste allowance so you do not run short mid-pour.
Quick reference: bags for common slabs (4 in thick, no waste)
| Slab size | Cubic yards | 80 lb bags |
|---|---|---|
| 4 x 4 ft | 0.20 | 9 |
| 8 x 8 ft | 0.79 | 36 |
| 10 x 10 ft | 1.23 | 56 |
| 12 x 12 ft | 1.78 | 80 |
Frequently asked questions
How many 80 lb bags of concrete make one cubic yard?
About 45 bags. One 80 lb bag yields roughly 0.60 cubic feet, and a cubic yard is 27 cubic feet.
Should I add extra for waste?
Yes. Most contractors add 5% to 10% for uneven ground, spillage and over-excavation.
When should I order ready-mix instead of bags?
Above about 1 cubic yard (roughly 45 bags), ready-mix is usually cheaper and easier. Many suppliers charge a short-load fee under 3 to 4 yards, so ask first.