4×4 slab: concrete by thickness
| Thickness | Cu ft | Cu yd | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 3.5″ | 4.67 | 0.17 | 8 | 11 |
| 4″ | 5.33 | 0.20 | 9 | 12 |
| 5″ | 6.67 | 0.25 | 12 | 15 |
| 6″ | 8.00 | 0.30 | 14 | 18 |
No waste included in the table.
Worked example
4 ft × 4 ft = 16 sq ft. At 4 inches: 16 × 4 ÷ 12 = 5.33 cu ft, or 0.20 cubic yards. With 10% extra that is 0.22 yd³, or 10 bags of 80 lb mix.
At this size, bagged mix is manageable by hand.
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 4×4 slab?
9 × 80 lb or 12 × 60 lb bags at 4 inches thick, before waste.
How many yards of concrete for a 4×4 slab?
0.20 cubic yards at 4 inches; 0.30 at 6 inches.