How Many Bags of Concrete for 4 Fence Posts?
Setting 4 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 4 fence posts comes to about 8 bags of 80 lb mix, or 11 bags of 60 lb.
Concrete calculator →Bags by post and hole size for 4 posts
| Post | Hole | Depth | Cu ft per hole | 80 lb bags (all) | 60 lb bags (all) |
|---|---|---|---|---|---|
| 4x4 | 10 in | 24 in | 0.92 | 7 | 9 |
| 4x4 | 10 in | 30 in | 1.15 | 8 | 11 |
| 4x4 | 12 in | 36 in | 2.10 | 15 | 19 |
| 6x6 | 14 in | 36 in | 2.58 | 18 | 23 |
| 6x6 | 16 in | 42 in | 4.15 | 28 | 37 |
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 6 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.
Gravel at the bottom
Put 3 to 6 inches of gravel under each post for drainage and tamp it. Crown the concrete at the top so rain runs off instead of pooling against the wood.
Related: How Many Bags of Concrete for 8 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 9 bags for 4 posts in 10-inch holes, and return what you do not open.
Questions people ask
How many 80 lb bags for 4 fence posts?
About 8 bags for 4x4 posts in 10-inch holes, 30 inches deep.
How many 60 lb bags for 4 fence posts?
About 11 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 4 6x6 posts?
About 18 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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