How Much Concrete for a 4×4 Post?
A 4×4 post in a 10-inch hole 24 inches deep takes 0.92 ft³ of concrete: 3 bags of 50-lb, 3 bags of 60-lb or 2 bags of 80-lb mix per post.
- Concrete per hole0.92 ft³
- 50-lb bags3
- 60-lb bags3
- 80-lb bags2
Concrete needed
0.92 cubic feet
0.034 yd³ · 0.026 m³ · no extra added
You need about 0.92 cubic feet of concrete, or 2 bags of 80 lb mix.
Bags of premix
- 440 lb bags
- 350 lb bags
- 360 lb bags
- 280 lb bags
- —20 kg bags
- —25 kg bags
- Before extra0.03 yd³ (0.9 ft³)
- Weight of bags160 lb
- Per hole0.92 ft³ · 2 × 80 lb
- Ready-mix costAdd a price per yd³
- Bagged costAdd a price per bag
One 80 lb bag makes about 0.60 ft³ (manufacturer's published yield). Bags are rounded up.
Bagged mix makes sense at 0.03 yd³. A ready-mix truck for a load this small would usually come with a minimum-order or short-load charge.
Estimate only, not a quote or engineering advice. Disclaimer
Fence posts, mailbox posts and light gate posts are usually 4×4s, which measure 3.5 × 3.5 inches.
Bags per 4×4 post by hole size
| Hole diameter × depth | ft³ | 50-lb | 60-lb | 80-lb |
|---|---|---|---|---|
| 8 × 24 in | 0.53 | 2 | 2 | 1 |
| 10 × 24 in | 0.92 | 3 | 3 | 2 |
| 10 × 30 in | 1.15 | 4 | 3 | 2 |
| 12 × 30 in | 1.75 | 5 | 4 | 3 |
| 12 × 36 in | 2.10 | 6 | 5 | 4 |
How the post changes the answer
A 4×4 post takes up 0.085 ft³ for every foot it sits in the hole, so the calculator subtracts it. In a 10 × 24 in hole the post displaces 0.17 ft³, the yield of about 0.5 bags of 50-lb mix.
Hole size
QUIKRETE's fence-post directions call for a hole about three times the post's width and about a third of the post's length deep. For a 4×4 that is roughly a 11-inch hole. For gates, decks and anything that carries a structure, check local code and frost depth, which may require deeper or wider footings.
For a whole fence, set the number of holes in the calculator above. See also concrete for a 6×6 post.
Frequently asked questions
How many bags of concrete for a 4x4 post?
In a 10-inch hole 24 inches deep: 3 bags of 50-lb, 3 bags of 60-lb or 2 bags of 80-lb mix. Bigger holes take more; see the table.
What size hole for a 4x4 post?
A common rule, from QUIKRETE’s directions, is a hole about 3 times the post width (about 11 inches for a 4×4) and about one-third of the post’s length deep. Local code can require more for structural posts.
Do I put gravel under a fence post?
Many builders put a few inches of gravel in the bottom for drainage. If you do, enter its depth in the calculator and it is left out of the concrete.
Other posts
Related
Sources
- QUIKRETE: Concrete Mix No. 1101 data sheet (Revised Oct 2022; checked Nov 11, 2026)