How many bags of concrete for a 24x24 slab, 4 inches thick?
A 24x24 slab 4 inches thick needs 192.0 cubic feet (7.11 cubic yards) of concrete: about 352 bags of 80 lb mix with 10% extra.
That is over a cubic yard. A ready-mix truck delivery (about 7.82 yards) is usually cheaper and easier than mixing 352 bags by hand.
| Bag size | Exact | With 10% extra |
|---|---|---|
| 80 lb | 320 | 352 |
| 60 lb | 427 | 470 |
| 50 lb | 512 | 564 |
| 40 lb | 640 | 704 |
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.