24×30 slab: concrete by thickness
| Thickness | Cu ft | Cu yd | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 3.5″ | 210.00 | 7.78 | 350 | 467 |
| 4″ | 240.00 | 8.89 | 400 | 534 |
| 5″ | 300.00 | 11.11 | 500 | 667 |
| 6″ | 360.00 | 13.33 | 600 | 800 |
No waste included in the table.
Worked example
24 ft × 30 ft = 720 sq ft. At 4 inches: 720 × 4 ÷ 12 = 240.00 cu ft, or 8.89 cubic yards. With 10% extra that is 9.78 yd³, or 440 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 24×30 slab?
400 × 80 lb or 534 × 60 lb bags at 4 inches thick, before waste.
How many yards of concrete for a 24×30 slab?
8.89 cubic yards at 4 inches; 13.33 at 6 inches.