How to use this calculator
- 1Choose panel fence or post-and-rail / picket.
- 2Enter the total fence length, the number of straight sides and any gates.
- 3Enter the fence height and the panel width or post spacing.
- 4Enter the post hole size to see the post length and the concrete needed.
The formula
- 01Spacing = panel width + post width (panel fence) or post spacing
- 02Fence without gates = total length − gates × gate width
- 03Sections = fence without gates ÷ spacing, rounded up, + (sides − 1) + gates
- 04Posts = sections + 1 + gates + extra posts
- 05Pickets = fence without gates ÷ (picket width + gap), rounded up, + (sides − 1) + gates
- 06Post length = fence height + hole depth
- 07Concrete per hole = π × (hole Ø ÷ 2)² × depth − post area × depth
A straight run always has one more post than sections. The last panel or section may need cutting down, which is why the count rounds up.
Each corner and each gate starts a new run, and every run can end in a part-panel. However the length is shared out between the sides, rounding each run up adds at most one section per extra run, so adding one per corner and one per gate is never short. Each gate splits a run, which also adds one post; the two posts either side of the gate are the gate posts.
Post concrete is the hole volume minus the part the post fills. Each post has to reach from the bottom of its hole to the top of the fence, so the post length is the fence height plus the hole depth.
Worked example
A 20 m fence with 1.83 m panels and 100 mm posts needs 11 panels and 12 posts.
For a 1.8 m fence in 600 mm holes, each post is 2.4 m long.
Holes 300 mm wide and 600 mm deep need 0.481 m³ of concrete — 42 bags of 25 kg.
Tips before you buy
- Set the first and last posts, run a string line between them, then set the rest.
- Slope the concrete away from the post at the top so rain runs off.
- Check boundary lines and any height limits before you build.
- Measure each side on its own: if you know every side's length, run the calculator once per side for the tightest panel count.
Frequently asked questions
How many fence posts do I need?
For a straight run: the number of sections plus one. With corners and gates, enter the number of straight sides and gates — each gate adds a post, and the corners share their posts.
How deep should fence posts be?
A common rule is to bury about a third of the post: 600 mm of a 2.4 m post for a 1.8 m fence, or 2 ft of an 8 ft post for a 6 ft fence (Wickes suggests 450–600 mm holes for posts up to 8 ft). Some guides go deeper, and you must go below the frost line where the ground freezes. Local advice comes first.
How long should fence posts be?
The fence height plus the hole depth: a 1.8 m fence with 600 mm holes needs 2.4 m posts (a 6 ft fence with 2 ft holes needs 8 ft posts).
Why does the calculator add panels for corners?
Each side usually ends in a part-panel that has to be cut, and an offcut from one side is rarely the right size for the next. Allowing one extra panel per corner and per gate means you won't run short.
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Sources
- Method: sections + 1 posts; post concrete = hole volume − post volume. Bag yields as in the concrete calculator.
- This Old House – All about wood fences: bury at least one-third of each post
- Wickes – How to install a fence: 450–600 mm post holes for posts up to 8 ft
- Family Handyman – How to build a privacy fence: at least three 2 × 4 rails or two 2 × 6s
- Jacksons Fencing – How to measure for a garden gate: about 10 mm gap each side
Formulas last reviewed: September 30, 2026 ·How we check our formulas