5×5 slab: concrete by thickness
| Thickness | Cu ft | Cu yd | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 3.5″ | 7.29 | 0.27 | 13 | 17 |
| 4″ | 8.33 | 0.31 | 14 | 19 |
| 5″ | 10.42 | 0.39 | 18 | 24 |
| 6″ | 12.50 | 0.46 | 21 | 28 |
No waste included in the table.
Worked example
5 ft × 5 ft = 25 sq ft. At 4 inches: 25 × 4 ÷ 12 = 8.33 cu ft, or 0.31 cubic yards. With 10% extra that is 0.34 yd³, or 16 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 5×5 slab?
14 × 80 lb or 19 × 60 lb bags at 4 inches thick, before waste.
How many yards of concrete for a 5×5 slab?
0.31 cubic yards at 4 inches; 0.46 at 6 inches.