12×12 slab: concrete by thickness
| Thickness | Cu ft | Cu yd | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 3.5″ | 42.00 | 1.56 | 70 | 94 |
| 4″ | 48.00 | 1.78 | 80 | 107 |
| 5″ | 60.00 | 2.22 | 100 | 134 |
| 6″ | 72.00 | 2.67 | 120 | 160 |
No waste included in the table.
Worked example
12 ft × 12 ft = 144 sq ft. At 4 inches: 144 × 4 ÷ 12 = 48.00 cu ft, or 1.78 cubic yards. With 10% extra that is 1.96 yd³, or 88 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 12×12 slab?
80 × 80 lb or 107 × 60 lb bags at 4 inches thick, before waste.
How many yards of concrete for a 12×12 slab?
1.78 cubic yards at 4 inches; 2.67 at 6 inches.