The quick answer: a straight 100 ft fence with posts 8 ft apart needs 14 posts. With posts 6 ft apart, you need 18 posts. Add one extra post for each gate and each change of direction that is not already counted.
This guide explains the formula, gives post counts for other fence lengths, and shows how much concrete, rails and boards to order. For your exact layout, use the fence calculator, which handles feet, metres and panel fences.
The fence post formula
Posts = (fence length ÷ post spacing), rounded up, + 1
For 100 ft at 8 ft spacing: 100 ÷ 8 = 12.5, which rounds up to 13 sections. Add one for the post at the far end, giving 14 posts. The extra one is needed because every section has a post at each end, and the sections share the posts between them.
Fence posts for other lengths
| Fence length | Posts at 6 ft spacing | Posts at 8 ft spacing |
|---|---|---|
| 25 ft | 6 | 5 |
| 50 ft | 10 | 8 |
| 75 ft | 14 | 11 |
| 100 ft | 18 | 14 |
| 150 ft | 26 | 20 |
| 200 ft | 35 | 26 |
These counts are for a single straight run. For a fence around three sides of a garden, add up the total length, work out the posts, then add one post for each corner. Each gate needs its own post on both sides, and gate posts should be heavier, such as 6 × 6 in instead of 4 × 4 in.
Metric and panel fences
In the UK, panels are usually 6 ft (1.83 m) wide. With a 100 mm post between each panel, each bay takes up about 1.93 m. For a 30 m run:
- Panels: 30 ÷ 1.93 = 15.5, so 16 panels (one cut down to fit)
- Posts: 16 + 1 = 17 posts
How much concrete per post?
A common setup is a 4 × 4 post in a hole 10 inches wide and about 30 inches deep. After taking away the space the post takes up, the hole holds about 1.15 cubic feet of concrete.
- 80 lb bags (about 0.6 cu ft each): 2 bags per post, so 28 bags for 14 posts.
- 50 lb fast-setting bags (about 0.375 cu ft each): 3 bags per post, so 42 bags.
- UK 20 kg postmix bags: typically 1–2 bags per post, depending on hole size.
As a rule of thumb, bury about one third of the post. A 6 ft high fence needs posts around 8–9 ft long, set about 2–3 ft into the ground. In areas where the ground freezes, the hole should go below the frost line.
Rails and fence boards
For a 100 ft wooden privacy fence with 8 ft sections:
- Rails: 2 rails per section for fences up to 4 ft high, 3 rails for a 6 ft fence. That is 13 × 3 = 39 rails of 8 ft.
- Boards (pickets): with 5.5 in boards fitted tight, each 8 ft section needs about 18 boards, so around 234 boards. Add 5–10% for splits and warped boards.
- Fixings: two nails or screws per board on each rail, so six per board on a 3-rail fence.
Common mistakes
- Forgetting the “+ 1” and ending up one post short.
- Not adding posts for gates, or using light posts to hang a gate.
- Measuring along a curved or sloped line and assuming it is straight.
- Setting posts too shallow, which lets the fence lean in strong wind.
Frequently asked questions
What is the best spacing for fence posts?
Most wooden fences use 6 to 8 ft spacing. Use 6 ft on windy or exposed sites or for heavy boards. Chain-link fences often use up to 10 ft, and panel fences follow the panel width.
How many fence posts for 200 feet?
26 posts at 8 ft spacing, or 35 posts at 6 ft spacing, for a straight run.
Do corner posts count as extra posts?
A corner post ends one straight run and starts the next. If you work out each side separately, count the corner post only once, not twice.
Can I use gravel instead of concrete?
Yes. Tightly packed crushed stone drains well and can make posts last longer, but concrete is stronger in soft soil and for gate posts.
Related: the DIY Project Budget & Materials Planner turns your measurements into quantities, costs and a shopping list.
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