How much concrete for fence posts
Select a post first, then provide the number of posts and the hole. The post is taken out of the hole before the bags needed for the entire fence are counted.
Concrete bags needed for each fence post
| Post | Hole width | Concrete depth | 50 lb bags | 60 lb bags | 80 lb bags |
|---|---|---|---|---|---|
| 4x4, 6 ft long | 10.5 in | 24 in | 4 | 3 | 2 |
| 4x4, 8 ft long | 10.5 in | 32 in | 5 | 4 | 3 |
| 4x4, 10 ft long | 10.5 in | 40 in | 6 | 5 | 4 |
| 6x6, 8 ft long | 16.5 in | 32 in | 10 | 9 | 7 |
| 6x6, 10 ft long | 16.5 in | 40 in | 13 | 11 | 8 |
| 6x6, 12 ft long | 16.5 in | 48 in | 15 | 13 | 10 |
| 4 in round, 8 ft long | 12 in | 32 in | 6 | 5 | 4 |
According to the Quikrete post-setting guide, each hole is 3 times as wide as its post. Concrete depth equals one third of the post's length, with 6 in of gravel below. Each 4x4 measures 3.5 in square. Each 6x6 measures 5.5 in. Each post's bag count includes 10% extra.
How much concrete do I need for a fence post?
Find the hole's volume first, then subtract the space filled by the post. A 4x4 occupies about 14% of a 10.5 in hole. Leaving the post out of your calculation adds roughly one extra bag for each group of seven.
Every post is filled separately, so leftover concrete from a partly used bag carries over to the next hole. As a result, the total for a fence line often falls below the number of bags per post multiplied by your number of posts.