Fence Calculator
Posts, panels, rails and pickets for a fence of any length.
Good to know. A fence always has one more post than panels. Forgetting it is a classic trip back to the shop.
Approximate. Real-world values vary.
How it works
In plain words
Divide the fence length by the post spacing and round up for the number of sections. There is one more post than sections, and each corner or separate run adds another. Pickets are the length divided by one picket’s width plus its gap.
The formula
sections = ⌈length ÷ spacing⌉ (+1 per corner) posts = sections + 1 rails = sections × rails per section pickets = ⌈length ÷ (picket width + gap)⌉
Worked example
30 m ÷ 1.83 m is 16.4, so 17 sections and 18 posts. Two rails a section is 34 rails, and 3,000 cm ÷ (9 + 1) cm is 300 pickets.
Sources
No outside data or rates: this is plain arithmetic.
4 automated tests check its answers on every change.
About the fence calculator
Planning a fence starts with three numbers: the total length, the spacing between posts and how many corners there are. From those, the calculator works out the posts, the sections between them, the rails that hold the pickets or boards, and the number of pickets.
Posts are usually 1.8 to 2.4 metres apart: 1.83 m (6 ft) for standard UK panels and 8 ft (2.44 m) for most US wood fences. Closer spacing makes a sturdier fence in windy places. Every run of fence needs a post at each end, so a fence has one more post than sections, and each corner, gate or separate run adds one more.
For picket or board fences, divide the length by the width of one picket plus the gap you want. A privacy fence has no gap, or overlapping boards; a traditional picket fence leaves a gap about a third of the picket width. Most fences need two rails per section up to about 1.2 m (4 ft) high and three for taller ones.
Buy a few extra pickets for cuts and knots, and check local rules on height and boundaries before you start. Each post also needs concrete or a spike; the concrete calculator works out post holes. A post is usually set a quarter to a third of its length in the ground.
Questions people ask
How many fence posts do I need?
The length divided by the post spacing, rounded up, plus one, plus one more for each corner. 30 m at 1.83 m spacing needs 18 posts.
How far apart should fence posts be?
Usually 1.8 to 2.4 m (6 to 8 ft). Standard UK panels are 1.83 m wide; US wood fences typically use 8 ft sections.
How deep should fence posts go?
About a third of the post’s above-ground height, and at least 60 cm (2 ft), deeper in frost-prone or windy places.