Fence Post Calculator: Posts & Concrete for a Fence Line

Enter your total fence length and the post spacing you plan to use (8 ft on-center is the most common). The calculator instantly returns how many fence posts you need, how many fence sections that creates, and how many bags of concrete to buy. That is all most people need. Open More options to switch to metric, set a custom post-hole diameter and depth, pick a different concrete bag size, or add prices for a quick material estimate.

A fence line is divided into equal sections between posts. The number of sections is the fence length divided by the post spacing, rounded up. Because every fence needs a post at both ends, the number of posts is always one more than the number of sections. So a 100 ft fence with posts 10 ft apart has 10 sections but 11 posts. Tighter spacing gives a stiffer, stronger fence but costs more posts and concrete; wider spacing saves materials but can sag. Most wood and vinyl fences use 6–8 ft spacing, while chain-link often runs up to 10 ft.

Sections = ceil(Fence length ÷ Post spacing)

Posts = Sections + 1

For concrete, each post sits in a hole. The concrete needed per post is the hole volume minus the post volume:

Concrete per post = (π × (hole diameter ÷ 2)² × hole depth) − (post width² × hole depth)

Total concrete is multiplied by the post count, then divided by the yield per bag (80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45 cu ft) and rounded up to whole bags.

Example 1 — Backyard privacy fence. A 120 ft fence with 8 ft spacing: 120 ÷ 8 = 15 sections, so 16 posts. With standard 10 in × 24 in holes and 4×4 posts, that is about 15 cu ft of concrete, or 25 bags of 80 lb mix.

Example 2 — Chain-link on a wide run. A 200 ft chain-link fence at 10 ft spacing: 200 ÷ 10 = 20 sections, so 21 posts. Corner and end posts get bigger holes, so buy a few extra bags.

Example 3 — Short garden fence. A 24 ft fence at 6 ft spacing: 24 ÷ 6 = 4 sections, 5 posts.

- Always add the end post. Forgetting the +1 is the most common fence-post mistake.
- Add posts for corners and gates. Each corner and each side of a gate needs its own post, and gate/corner posts should be set deeper.
- Bury one-third of the post. A 6 ft above-ground fence usually needs a 3 ft hole, so buy 8–9 ft posts.
- Round concrete up. Partial bags are wasted; it is cheaper to have one spare bag than to stop mid-pour.
- Widen holes in loose or sandy soil for a stronger footing — that raises your bag count.