How many fence posts do I need?
Divide the length by the spacing, then add one.
100 ft at 8 ft spacing is 14 posts; 200 ft is 26. The plus one is the post at the far end — leave it out and you are a post short on every run you price.
By length of run
| Run | 6 ft spacing | 8 ft spacing | 10 ft spacing |
|---|---|---|---|
| 50 ft | 10 | 8 | 6 |
| 100 ft | 18 | 14 | 11 |
| 150 ft | 26 | 20 | 16 |
| 200 ft | 35 | 26 | 21 |
| 300 ft | 51 | 39 | 31 |
| 500 ft | 85 | 64 | 51 |
These are straight runs with a post at each end. Every corner and every gate adds one more, because a corner post terminates two runs and cannot be shared the way a line post is.
By acreage
| Area | Perimeter | 6 ft | 8 ft | 10 ft |
|---|---|---|---|---|
| 1 acre | 835 ft | 140 | 105 | 84 |
| 2 acres | 1181 ft | 197 | 148 | 119 |
| 3 acres | 1446 ft | 241 | 181 | 145 |
| 5 acres | 1867 ft | 312 | 234 | 187 |
| 10 acres | 2640 ft | 440 | 330 | 264 |
An acre is 43,560 sq ft, which as a square is 209 ft a side and 835 ft of perimeter. That is the best case: a square encloses more area per foot of fence than any other rectangle, so a long thin acre needs considerably more. Ten acres in one square block takes 330 posts — only 3.1 times as many as one acre, for ten times the land. Perimeter grows as the square root of area, which is why fencing gets cheaper per acre the more you fence.
Choosing the spacing
Eight feet is the default because most panels and rails are sold in 8 ft lengths, so it wastes nothing. Six feet is for heavy panels, high wind or stock that leans; ten is for wire where the posts only carry tension, not a surface.
The spacing decides the cost more than the post does. Going from 8 ft to 6 ft on a 200 ft fence is 9 extra posts and the concrete for each — before any panels. Going the other way to 10 ft saves 5 posts, and buys a fence that flexes in wind.
Common questions
- Do I count the corner posts twice?
- No — a corner post ends one run and starts the next, so count it once and then add one for each corner overall. A rectangular yard fenced on all four sides needs exactly as many posts as it has 8 ft gaps, with no plus one, because the run closes on itself.
- How many posts for 100 feet?
- 14 at 8 ft spacing, 18 at 6 ft. If that 100 ft has a gate in it, add one: a gate needs its own post at each side and neither can be a shared line post.
- How many for an acre?
- About 105 at 8 ft spacing, if the acre is square. If it is a long strip the perimeter can easily be half as much again, so measure the actual boundary rather than working from the area.
- Does the spacing have to be exact?
- Spread the remainder rather than leaving one short bay at the end. A 100 ft run at 8 ft leaves 4 ft over; 13 bays of 7.7 ft looks deliberate and a 4 ft stub does not.
- What about slopes?
- Measure along the ground, not across the map. A slope adds real distance — a 100 ft run down a 10% grade is about 100.5 ft of fence, which is not enough to matter, but a steep bank is, and stepped panels need a post at every step regardless of spacing.