How many bags of concrete for a 4x8 slab, 6 inches thick?
A 4x8 slab 6 inches thick needs 16.0 cubic feet (0.59 cubic yards) of concrete: about 30 bags of 80 lb mix with 10% extra.
| Bag size | Exact | With 10% extra |
|---|---|---|
| 80 lb | 27 | 30 |
| 60 lb | 36 | 40 |
| 50 lb | 43 | 47 |
| 40 lb | 54 | 59 |
Typical yields: 80 lb bag 0.60 cu ft, 60 lb 0.45, 50 lb 0.375, 40 lb 0.30. Check your bag; brands vary slightly. The 10% covers spills, uneven ground and form flex.