Fence Post Hole Calculator
Estimate concrete needed for fence post holes.
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.
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.