Fence Post and Concrete Calculator
Enter fence length and post size to get posts and bags of concrete.
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Fence Post and Concrete Calculator by TheCalcTools
How the Fence Post and Concrete Calculator works
Posts = fence length ÷ spacing, plus one, plus corners and gate posts.
Dig the hole about one third of the post’s above-ground height plus 6 inches, and below the frost line where needed.
Concrete per post is the hole volume minus the post volume. A bag’s yield is taken as 0.45 or 0.6 cubic feet.
The formula
Worked example
Using the default values shown in the calculator:
| Fence length (ft) | 120 |
|---|---|
| Post spacing (ft) | 8 |
| Corner or end posts | 4 |
| Gates | 1 |
| Fence height above ground (ft) | 6 |
| Post hole diameter (in) | 10 |
| Post width (in) | 3.5 |
| Concrete bag size | 80 lb bag (0.60 cu ft) |
- 120 ft ÷ 8 ft = 15 sections, so 16 posts + 4 corners + 1 gate = 21 posts.
- Hole depth 30 in, 1.15 cu ft of concrete per post, 41 bags in total.
Result:
| Posts needed | 21 |
|---|---|
| Hole depth (in) | 30 |
| Post length to buy (ft) | 8.5 |
| Concrete per post (cu ft) | 1.15 |
| Bags of concrete per post | 1.9 |
| Bags of concrete in total | 41 |
Frequently asked questions
How deep should fence posts be?
A common rule is one third of the post’s total length in the ground, and below the local frost line in cold climates. Check local rules.
How many bags of concrete per post?
Usually 2 to 3 bags of 80 lb for a 6 ft fence post in a 10 inch hole.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.