Post hole concrete calculator
You need
– cubic yards
– cu ft · – m³ · sq ft
- Ready-mix concrete ($160–$195/yd)
- –
- Installed by a contractor
- –
Short answer
QUIKRETE's rule: dig the hole 3 times the post's width, and a third of the post's total length deep plus 6 inches for gravel. For a 4×4 post on a 6 ft fence that's a 10.5-inch hole about 42 inches deep, which takes about 4 bags of 50 lb mix (3 of 80 lb) per post.
| Hole diameter | 3× the post width[1] |
|---|---|
| Hole depth | ⅓ of post length + 6 in gravel[1] |
| Fill to | 3–4 in below the top[1] |
| Gravel base | 6 in at the bottom of the hole[2] |
| Local codes | may set a minimum depth (e.g. 30 in)[2] |
| 4×4 post, 6 ft fence | 1.42 cu ft per hole |
How the post hole math works
The calculator takes the hole volume between the gravel layer and 3 inches below grade, then subtracts the post. QUIKRETE suggests stopping the concrete 3–4 inches below the top and backfilling with soil. A 4×4 post is actually 3.5 inches square and a 6×6 is 5.5 inches.
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Frequently asked questions
How many bags of concrete per 4×4 post?
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About 4 bags of 50 lb mix or 3 bags of 80 lb mix for a 6 ft fence with a 10.5-inch hole, 42 inches deep with 6 inches of gravel.
How deep should a fence post hole be?
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QUIKRETE recommends a third of the post's overall length plus 6 inches for gravel. Posts that carry structural loads, like deck posts, must go at least 6 inches below the frost line.
Sources
- [1]QUIKRETE, Project: Setting Posts (project sheet, checked October 5, 2026)
- [2]Bob Vila, How to Install Fence Posts (updated September 17, 2020)
- [3]QUIKRETE, Concrete Mix No. 1101 data sheet (bag yields) (current data sheet)
Prices are national ranges published by the sources above, not quotes. Your price depends on size, access, site preparation and local labor rates. The only way to know is to compare written quotes.