How many bags of concrete do I need?
Short answer
A 10 × 10 ft slab 4 inches thick takes about 1.36 cubic yards with 10% extra: 62 bags of 80 lb, 82 of 60 lb or 123 of 40 lb. A full cubic yard takes 45 bags of 80 lb.
Work it out for your numbers
Concrete needed
1.36 cubic yards
- 80 lb bags
- 62 bags
- 60 lb bags
- 82 bags
- 40 lb bags
- 123 bags
- Volume
- 36.7 cubic feet
Bags by slab size
| Slab | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|
| 4 × 4 ft, 4 in thick | 0.22 | 10 | 14 |
| 10 × 10 ft, 4 in | 1.36 | 62 | 82 |
| 10 × 12 ft, 4 in | 1.63 | 74 | 98 |
| 12 × 12 ft, 4 in | 1.96 | 88 | 118 |
| 20 × 20 ft, 4 in | 5.43 | 245 | 326 |
Includes 10% extra for spillage and uneven ground.
The math
Length × width × thickness in feet (inches ÷ 12) gives cubic feet. Add 10%, then divide by what each bag makes: about 0.6 cubic feet for an 80 lb bag, 0.45 for 60 lb and 0.3 for 40 lb. Divide cubic feet by 27 for cubic yards.
How thick?
4 inches suits patios, walkways and shed pads. Driveways and anything carrying vehicles are often 5 to 6 inches. Check what your local code or permit requires.
Bags or a truck?
Bags make sense up to about a cubic yard. Beyond that, 45-plus bags of 80 lb is a lot of mixing, and the first batches can start setting before the last ones are poured. Ready-mix suppliers deliver “short loads” for small jobs, usually with a fee, which is often worth it.
Common questions
How many 80 lb bags of concrete are in a yard?
45. A cubic yard is 27 cubic feet and each 80 lb bag makes about 0.6 cubic feet.
How many bags of concrete for a 10x10 slab?
62 bags of 80 lb for a 4-inch slab, including 10% extra.
How much does an 80 lb bag of concrete cover?
About 0.6 cubic feet, which is 1.8 square feet at 4 inches thick.
Updated October 29, 2026. Figures are estimates for planning. Check product labels and local codes before you buy or build.