Fence Calculator: Posts, Rails and Pickets
Fence posts, rail length and pickets for a run of fence from its length and spacing.
Inputs
- Working
- 40 m ÷ 2.4 m = 16.67 → 17 sections, so 17 + 1 = 18 posts; rails 40 m × 3 + 5%
- Rail lumber (total)
- 126 m
- Pickets (est.)
- 400
- Perimeter
- 40 m
- A straight run with one end post each side. Each corner and gate post is extra unless it already falls on the spacing.
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What each Fence input means
- Fence perimeter
- The length of fence, in metres or feet. For several straight runs, enter each separately or add the lengths and then add a post for every corner.
- Post spacing
- Centre-to-centre distance between posts. Decks.com gives 6–8 ft (1.8–2.4 m) for wood and composite and 8–10 ft for vinyl; matching your rail length avoids cutting.
- Horizontal rails
- Horizontal rails per section: two for a low fence, three for a typical 6 ft privacy fence.
- Picket spacing, centre to centre
- Centre-to-centre picket spacing, in cm or inches: the picket's width plus the gap. Butt-jointed privacy pickets have no gap, so it is just their width.
- Waste allowance
- Extra rail length for cuts and joins.
- Units
- Metric (metres, m², litres) or US units (feet, square feet, gallons). The run length and spacings switch with it, so post spacing in feet or metres both work.
Fence formula
sections = length ÷ post spacing, rounded up · posts = sections + 1 · rail = length × rails × (1 + waste %) · pickets = length ÷ picket spacing
A straight fence is a row of sections, each spanning post to post. Divide the length by the post spacing and round up to get the sections; there is always one more post than sections, because both ends need one. Most residential wood and composite privacy fences set posts 6–8 ft (1.8–2.4 m) apart and vinyl 8–10 ft, per Decks.com — the rail length available often decides, since an 8 ft post spacing uses 8 ft rails without cutting. Each horizontal rail runs the full length, so the rail stock is the length times the number of rails, plus waste. Pickets are the length divided by their centre-to-centre spacing: picket width plus the gap.
Fence worked example
A 40 m run with posts every 2.4 m: 40 ÷ 2.4 = 16.7, so 17 sections and 18 posts. Three rails along 40 m is 120 m of rail, 126 m with 5% waste, and pickets at 10 cm centres need 400. In feet, a 130 ft run at 8 ft spacing is 16.25 sections — 17 — so 18 posts.
More Fence examples
A 100 ft run with posts 8 ft apart: 12.5 sections round up to 13, so 14 fence posts. Two rails make 210 ft of rail lumber with 5%, and 4-inch pickets with no gap need 300.
A 30 m garden boundary with posts every 1.8 m: 16.67 sections round up to 17, so 18 posts, and three rails come to 94.5 m with 5%.
Where the Fence calculator can give the wrong answer
- Corners and gates: each corner is a post that may not fall on the spacing, and each gate needs its own pair of heavier posts. Add them.
- A closed loop (a fenced square with no gaps) has as many posts as sections, not one more.
- On a slope the spacing is measured along the ground for stepped panels; posts get longer, not more numerous.
- Post depth and concrete are set by the fence height and local practice and are not calculated here.
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Fence reference table
| Fence length | Posts at 6 ft spacing | Posts at 8 ft spacing |
|---|---|---|
| 50 ft | 10 | 8 |
| 100 ft | 18 | 14 |
| 150 ft | 26 | 20 |
| 200 ft | 35 | 26 |
| 300 ft | 51 | 39 |
Fence FAQ
- Most residential privacy fences use 6–8 ft (1.8–2.4 m) for wood and composite and 8–10 ft for vinyl, according to Decks.com. Matching the spacing to standard rail lengths (8 ft) saves cutting.
- At 8 ft spacing, 100 ÷ 8 = 12.5, so 13 sections and 14 posts. At 6 ft it is 17 sections and 18 posts.
- Fence length ÷ picket spacing (picket width plus the gap). 100 ft is 1,200 inches; at 4 inches centre to centre that is 300 pickets.
- Each section needs a post at both ends, and neighbouring sections share one. A run of 13 sections has 14 posts; a closed loop shares its first and last, so it has 13.
- Work out each straight side on its own, then subtract one post for every corner, since neighbouring sides share it. Three sides of 40, 60 and 40 ft at 8 ft spacing take 6 + 9 + 6 = 21 posts, less 2 shared corners: 19.
- 50 ft is 600 inches. At 4-inch centres that is 150 pickets; at 6-inch centres — a 3½-inch picket with a 2½-inch gap — it is 100.