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10×20 slab: concrete by thickness
| Thickness | Cu ft | Cu yd | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 3.5″ | 58.33 | 2.16 | 98 | 130 |
| 4″ | 66.67 | 2.47 | 112 | 149 |
| 5″ | 83.33 | 3.09 | 139 | 186 |
| 6″ | 100.00 | 3.70 | 167 | 223 |
No waste included in the table.
Worked example
10 ft × 20 ft = 200 sq ft. At 4 inches: 200 × 4 ÷ 12 = 66.67 cu ft, or 2.47 cubic yards. With 10% extra that is 2.72 yd³, or 123 bags of 80 lb mix.
At over 1 cubic yard, compare the cost and labor of bags against a ready-mix delivery.
Assumes standard concrete mix bag yields: 80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45 cu ft. Check the yield on your bag. 1 cubic yard = 27 cubic feet.
Frequently asked questions
How many bags of concrete for a 10×20 slab?
112 × 80 lb or 149 × 60 lb bags at 4 inches thick, before waste.
How many yards of concrete for a 10×20 slab?
2.47 cubic yards at 4 inches; 3.70 at 6 inches.