Fence Post Calculator
Calculate the number of fence posts, post hole depth, concrete bags per hole, and total concrete needed based on fence length and post spacing.
ft
ft
ft
Number of Posts
—
Concrete Bags per Post —
Total Concrete Bags —
Extended More scenarios, charts & detailed breakdown ▾
ft
ft
ft
in
Line Posts
—
Bags per Hole —
Total Bags —
Total Concrete —
Professional Full parameters & maximum detail ▾
ft
ft
in
ft
in
Post Count
Line Posts —
Gate + Corner Posts —
Total Posts —
Hole & Concrete
Required Hole Depth —
Concrete per Hole —
Total Concrete —
Total 80 lb Bags —
How to Use This Calculator
- Enter your fence length in feet.
- Enter your post spacing (typically 8 ft).
- Enter the post hole depth in feet.
- Results show total posts, concrete per hole, and total bags needed.
Formula
Posts = floor(length ÷ spacing) + 1
Hole volume (ft³) = π × (diameter/2)² × depth | Bags = ceil(hole volume ÷ yield per bag)
Example
Example: 100 ft fence, 8 ft spacing, 3 ft deep holes → 14 line posts + 2 end posts = 13 posts, about 2 bags per hole, 26 total bags.
Frequently Asked Questions
- The general rule is to set posts at least 1/3 of their total length in the ground, or below the frost line — whichever is deeper. For a 6-ft fence with 8-ft posts, set them 2–2.5 ft deep minimum. In cold climates, frost lines can be 3–4 ft deep.
- For a 4×4 post in a 10" diameter hole at 24" depth, you need about 0.75 bags of 80 lb concrete. This calculator determines concrete volume based on your hole dimensions.
- Standard fence post spacing is 6–8 feet between posts. Using 8 ft spacing minimizes post count and works for most wood fence panels. Corner posts, gate posts, and end posts are additional.
- Yes — a 3–6 inch gravel base at the bottom of the hole improves drainage and reduces post rot. This calculator accounts for gravel base when calculating concrete volume.