Fence Post Hole Calculator
Estimate concrete needed for fence post holes.
Last updated 2026-08-21
What Is a Fence Post Hole Calculator?
The fence post hole calculator estimates how much concrete you need to set your fence posts. Enter the hole depth and diameter and the number of posts, and it returns the concrete volume and the number of 60 lb bags to buy.
How It Works
Concrete per hole = π × (Hole diameter ÷ 2 ÷ 12)² × Depth − (4/12)² × Depth. Bags = ceil(Total ÷ 0.45).
Example
12 posts, 12 in holes, 3 ft deep: 2.02 cu ft per hole → 24.3 cu ft → 54 × 60 lb bags.
How to Calculate
- Determine the hole depth, typically 24 to 30 in for a 6 ft fence, and the hole diameter, often 12 in for a 4×4 post.
- Enter the post depth, hole diameter, and number of posts. For 12 posts, 12 in holes, and 3 ft deep, each hole holds about 2.02 cu ft.
- Read the total concrete volume. At 2.02 cu ft per hole, 12 posts need about 24.3 cu ft.
- Check the bag count. Each 60 lb bag yields about 0.45 cu ft, so 24.3 cu ft needs 54 bags.
- Set the posts plumb in the holes, pour the concrete, and let it cure before attaching the fence.
Concrete Bags per Post Hole
| Hole Diameter | Hole Depth | Volume per Hole | 60 lb Bags per Post |
|---|---|---|---|
| 8 in | 24 in | 0.70 cu ft | 2 bags |
| 10 in | 24 in | 1.09 cu ft | 3 bags |
| 12 in | 24 in | 1.57 cu ft | 4 bags |
| 12 in | 30 in | 1.96 cu ft | 5 bags |
| 12 in | 36 in | 2.36 cu ft | 6 bags |
Sources
Frequently Asked Questions
How wide should the hole be?
A common rule is 3× the post width — a 12 in hole for a 4×4 post.
How much concrete per post?
One 50–60 lb bag is typical for a 4×4 post set 24–30 in deep.
Do I need concrete at all?
Concrete gives strong, durable anchoring. Gravel-and-tamp is faster but less rigid.
Estimate the cost with the Fence Cost Calculator or browse Fence Calculators