How Many Bags of Concrete for 12 Fence Posts?
Setting 12 posts takes more concrete than most people expect. With a typical 10-inch hole, 30 inches deep, around a 4x4 post, how many bags of concrete for 12 fence posts comes to about 24 bags of 80 lb mix, or 31 bags of 60 lb.
Concrete calculator →Bags by post and hole size for 12 posts
| Post | Hole | Depth | Cu ft per hole | 80 lb bags (all) | 60 lb bags (all) |
|---|---|---|---|---|---|
| 4x4 | 10 in | 24 in | 0.92 | 19 | 25 |
| 4x4 | 10 in | 30 in | 1.15 | 24 | 31 |
| 4x4 | 12 in | 36 in | 2.10 | 43 | 57 |
| 6x6 | 14 in | 36 in | 2.58 | 52 | 69 |
| 6x6 | 16 in | 42 in | 4.15 | 84 | 111 |
Volumes subtract the post (3.5 or 5.5 inches square) from a round hole and assume 0.60 cu ft per 80 lb bag and 0.45 per 60 lb bag.
Related: How Many Bags of Concrete for 4 Fence Posts?
Hole size rules of thumb
Many installers dig holes around three times as wide as the post and bury about one-third of the post. In cold climates, going below frost depth keeps posts from heaving. Corners, ends and gate posts take the most load and deserve the largest holes.
Gravel at the bottom
A few inches of gravel in the bottom of each hole lets water drain away from the end of the post, which helps wood posts last longer. Shape the top of the concrete so it slopes away from the post.
Related: How Many Bags of Concrete for 6 Fence Posts?
Fast-setting mix or regular
For many posts, regular concrete mixed in batches is economical; fast-setting mix saves time when you want to keep moving down the line. Either way, brace each post plumb until the concrete sets. See fast-setting concrete for posts.
Buy a few extra
Holes are rarely dug to the exact size. Add about 10 percent to the bag count, or 27 bags for 12 posts in 10-inch holes, and return what you do not open.
Questions people ask
How many 80 lb bags for 12 fence posts?
About 24 bags for 4x4 posts in 10-inch holes, 30 inches deep.
How many 60 lb bags for 12 fence posts?
About 31 bags for the same holes.
How big should a fence post hole be?
About three times the post width, deep enough for roughly a third of the post length or below frost depth.
How many bags for 12 6x6 posts?
About 52 bags of 80 lb mix in 14-inch holes, 36 inches deep.
Should I put gravel under fence posts?
Yes, a few inches of gravel at the bottom helps drainage.
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