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12×24 slab: concrete by thickness
| Thickness | Cu ft | Cu yd | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 3.5″ | 84.00 | 3.11 | 140 | 187 |
| 4″ | 96.00 | 3.56 | 160 | 214 |
| 5″ | 120.00 | 4.44 | 200 | 267 |
| 6″ | 144.00 | 5.33 | 240 | 320 |
No waste included in the table.
Worked example
12 ft × 24 ft = 288 sq ft. At 4 inches: 288 × 4 ÷ 12 = 96.00 cu ft, or 3.56 cubic yards. With 10% extra that is 3.91 yd³, or 176 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 12×24 slab?
160 × 80 lb or 214 × 60 lb bags at 4 inches thick, before waste.
How many yards of concrete for a 12×24 slab?
3.56 cubic yards at 4 inches; 5.33 at 6 inches.