How Many Bags of Concrete for 30 Fence Posts?
How many bags of concrete for 30 fence posts: about 58 bags of 80 lb mix if each 4x4 post sits in a 10-inch hole 30 inches deep. Each of those holes holds roughly 1.15 cubic feet of concrete after you subtract the post itself.
Concrete calculator →Bags by post and hole size for 30 posts
| Post | Hole | Depth | Cu ft per hole | 80 lb bags (all) | 60 lb bags (all) |
|---|---|---|---|---|---|
| 4x4 | 10 in | 24 in | 0.92 | 47 | 62 |
| 4x4 | 10 in | 30 in | 1.15 | 58 | 77 |
| 4x4 | 12 in | 36 in | 2.10 | 106 | 141 |
| 6x6 | 14 in | 36 in | 2.58 | 129 | 172 |
| 6x6 | 16 in | 42 in | 4.15 | 208 | 277 |
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
A common guideline is a hole about three times the post width and deep enough to bury roughly a third of the post’s total length, or to below the frost line where frost heave is a concern. Gate posts and corner posts usually get bigger, deeper holes.
Drainage under the post
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
Fast-setting post mix is poured dry into the hole and soaked with water, which is handy on a long fence line. Regular mix is premixed in a wheelbarrow and is usually cheaper per cubic foot. Check the bag’s yield, since post mixes can differ from standard concrete. 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 64 bags for 30 posts in 10-inch holes, and return what you do not open.
Questions people ask
How many 80 lb bags for 30 fence posts?
About 58 bags for 4x4 posts in 10-inch holes, 30 inches deep.
How many 60 lb bags for 30 fence posts?
About 77 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 30 6x6 posts?
About 129 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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