Fence posts
Fence post calculator: count, spacing, and depth.
Estimate how many posts you need, how deep to set them, the post length to buy, and bags of concrete per hole. A 100 ft fence at 8 ft spacing needs about 14 posts.
100 ft at 8 ft
14 posts
28 bags concrete
6 ft fence depth
2.0 ft
1/3 rule, 2 ft min
Post length
8.0 ft
height + buried
Depth by fence height
How deep and how long, by fence height
Buried depth uses the one-third rule with a 2 ft minimum. Post length is height plus buried depth — buy posts at least this long. Frost line can require deeper holes.
| Fence height | Buried depth | Post length |
|---|---|---|
| 4 ft | 2.0 ft | 6.0 ft |
| 6 ft | 2.0 ft | 8.0 ft |
| 8 ft | 2.7 ft | 10.7 ft |
Concrete per hole
For exact bags by hole diameter and depth, take your post count into the post-hole concrete calculator. Many people use fast-setting concrete for fence posts.
Formula shown
How the post estimate works
1. Post count
posts = ceil(length / spacing) + 1
2. Buried depth and post length
buried = max(height / 3, 2 ft); post = height + buried
3. Concrete per post
cubic feet = pi x (hole radius)^2 x buried depth; bags = ceil(/ bag yield)
Sources
- Fence post setting practice — post spacing and burial depth norms
- Quikrete fence post guidance — concrete per post hole and fast-set use
Sources checked
Checked against
Deck and fence layout rules and installed-cost ranges checked against published building and cost guides.
How we check our numbersLast updated: June 26, 2026
FAQ
Fence post questions
Post depth, spacing, concrete per post, and post count for common fence lengths.
How deep should fence posts be? + -
A common rule is to bury about one-third of the above-ground height, with a 2 ft minimum. A 6 ft fence post is often set about 2 ft deep, using an 8 ft post. In cold climates, set below the frost line, which can be deeper.
How far apart should fence posts be? + -
Wood fence posts are commonly 6 to 8 ft apart. Eight feet is a typical maximum; closer spacing is stronger. Match the spacing to your rail length and wind exposure.
How many bags of concrete per fence post? + -
It depends on the hole size and depth. For a 10 in hole about 2 ft deep, the calculator estimates about 2 bags of 80 lb concrete per post. Wider or deeper holes use more. Fast-setting concrete is often used for fence posts.
How many posts do I need for a 100 ft fence? + -
At 8 ft spacing, a straight 100 ft fence needs about 14 posts (one per section plus a closing post). Add a post for each corner, gate, and end.