Fence Post Concrete Calculator — Bags Per Post
Estimate concrete bags per fence post hole. Supports 4×4 and 6×6 wood posts plus chain link metal posts in 8, 10, and 12-inch diameter holes.
Enter Dimensions
Typically 1/3 of post height above grade
Results
Bags per Post
5bags
Total Bags
50bags
Volume per Hole
1.909cu ft
Concrete per post hole
Total Volume
19.09cu ft
All post holes combined
Editorial Standards
Each calculator is reviewed for formula accuracy, unit consistency, and alignment with current U.S. building practices before publication. We verify outputs against published engineering references and real-world project data. Learn more about our methodology.
Concrete sets fence posts permanently — done right, posts last decades; done wrong, they lean within a year. The two biggest estimation errors are (1) sizing the hole too small, leaving insufficient lateral support, and (2) forgetting that the post itself displaces concrete inside the hole.
This calculator solves both. Enter your hole dimensions and post size; it returns the exact concrete volume (in cubic feet) plus the 60 lb and 80 lb bag count needed per post and for the entire project.
How to Calculate Concrete for Fence Posts
Concrete per post = π × (Hole Diameter ÷ 24)² × Depth × 12 − (Post Width ÷ 12)² × Depth × 12, all in cubic feet. Bags = ⌈Concrete ÷ 0.60⌉ for 80 lb mix.
Common Post-Hole Configurations
- 4×4 wood post, 10″ hole × 32″ deep: 1.2 cu ft concrete ≈ 2 bags of 80 lb fast-set.
- 6×6 wood post, 12″ hole × 36″ deep: 2.1 cu ft ≈ 4 bags of 80 lb.
- 2-3/8″ metal post (chain link), 8″ hole × 30″ deep: 0.83 cu ft ≈ 2 bags of 60 lb.
- 4″ metal post (commercial gate), 14″ hole × 42″ deep: 3.1 cu ft ≈ 6 bags of 80 lb or ready-mix.
Frequently Asked Questions
How many bags of concrete per fence post?
For a 4×4 wood post in a 10″ hole 2 ft 8 in deep: ~2 bags of 80 lb fast-set per post. For a 6×6 post in a 12″ × 3 ft hole: 4 bags of 80 lb per post.
Should I use fast-setting or standard concrete for fence posts?
Fast-setting (Quikrete fast-set) is the easier choice — pour dry, add water, and post is rigid in 20–40 minutes. Standard 4000 psi mix takes 24+ hours to set and requires you to brace each post overnight.
Can I dry-pour concrete in a fence post hole?
Yes, for fast-set mixes only. Set the post plumb, fill hole with dry product, add water. Standard concrete must be mixed wet before placing.
How wide should a fence post hole be?
Three times the post width — a 4×4 (3.5″) post needs a 10–12″ hole; a 6×6 (5.5″) post needs a 16–18″ hole. Narrower holes save concrete but reduce lateral support against wind.
Does the post displace concrete in the calculation?
Yes — this calculator subtracts the underground portion of the post from total hole volume. For a 4×4×8 ft post buried 32 in deep, the post displaces ~0.27 cu ft of concrete.
Looking for the general calculator?
Calculate how many bags of concrete you need per fence post hole. Supports 4×4 and 6×6 wood posts plus metal pipe posts in standard hole sizes.
Open the Concrete Fence Post Calculator: Bag Count →