How many bags of concrete for a 12x16 slab, 6 inches thick?
A 12x16 slab 6 inches thick needs 96.0 cubic feet (3.56 cubic yards) of concrete: about 176 bags of 80 lb mix with 10% extra.
That is over a cubic yard. A ready-mix truck delivery (about 3.91 yards) is usually cheaper and easier than mixing 176 bags by hand.
| Bag size | Exact | With 10% extra |
|---|---|---|
| 80 lb | 160 | 176 |
| 60 lb | 214 | 235 |
| 50 lb | 256 | 282 |
| 40 lb | 320 | 352 |
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.