Fence posts & rails Calculator: measuring notes and method
Draw every independent run
Count each straight run and mark gates, corners and changes in level. A corner post shared by two runs can be counted twice if both runs are entered independently; reconcile the final post list.
Check rail lengths
The rail count is bays multiplied by rails per bay. It does not convert rails into purchasable stock lengths or account for joints. Check the actual bay spacing against the available rail lengths.
CHECK A PRACTICAL EXAMPLE
Why an extra metre can add another bay
Compare two straight runs using an illustrative maximum spacing of 2.4 m and three rails per bay.
12 m run
- Posts
- 6
- Rails
- 15
13 m run
- Posts
- 7
- Rails
- 18
The count changes at a bay boundary. The tool includes both end posts on each independent run; reconcile shared corners and gates when combining runs.
Fixed comparison in metric units. Values are illustrative unless linked to a recorded project; changing the calculator above does not change this example.
Formula
Bays = fence length ÷ maximum spacing, rounded up. Posts = bays + 1. Rails = bays × rails per bay.
Worked examples in metric and imperial units
Illustrative values match Reset example and stay fixed when you edit the calculator. Both columns describe the same calculation; converted inputs are rounded.
Metric worked example
- Straight fence length
- 20 m
- Maximum post spacing
- 2.4 m
- Rails per bay
- 3
Posts: 10
Imperial worked example
- Straight fence length
- 65.6168 ft
- Maximum post spacing
- 7.874 ft
- Rails per bay
- 3
Posts: 10
Follow the calculation
Lengths in this working are in metres.
- Bays = 20 ÷ 2.4, rounded up.
- Posts = whole bays + 1. Rails = whole bays × 3.
- Equal bay width = 20 m ÷ whole bays.
Reviewed 19 October 2026. How calculations are checked · Report a correction