How Many Bags of Concrete per Fence Post?
A 4×4 post set in a 10-inch hole 2 ft deep takes about 2.5 bags of 50 lb fast-setting concrete or about 1.5 bags of 80 lb standard mix.
Bags per post by hole size (4×4 post)
| Hole | Concrete volume | 50 lb fast-setting (0.375 cu ft) | 80 lb mix (0.6 cu ft) |
|---|---|---|---|
| 8" × 24" deep | 0.53 cu ft | 1.4 | 0.9 |
| 10" × 24" deep | 0.92 cu ft | 2.5 | 1.5 |
| 10" × 30" deep | 1.15 cu ft | 3.1 | 1.9 |
| 12" × 24" deep | 1.4 cu ft | 3.7 | 2.3 |
| 12" × 36" deep | 2.1 cu ft | 5.6 | 3.5 |
The volume subtracts the space taken by the 3½-inch post. A few inches of gravel at the bottom of the hole for drainage reduces the concrete slightly.
Fast-setting or standard mix?
Fast-setting mixes are poured dry into the hole and then soaked with water — no mixing, and the post can bear a load within hours. Standard mix is mixed first and needs longer to cure before you hang rails and pickets, but it costs less per cubic foot.
Total the concrete for a whole fence with the fence calculator.