GRAND CALCULATE · CENTRE-TO-CENTRE MARKS
Free Fence & Railing Post Spacing Calculator
Set out fence, railing or balustrade posts accurately along a straight run.
Enter the overall length, choose your required end offsets and spacing limits, and calculate the post positions.
GrandVerify provides individual set-out measurements from either end of the run, helping installers mark out post centres before installation.
IN THE WORKSHOP
How to set out fence or railing posts
- Measure the full straight run. Enter the distance from each end of the run to the centre of its nearest post. These end offsets can differ; enter zero if the centre falls on the end mark.
- Choose maximum spacing if bays must be no wider than your limit, or minimum spacing if they must be at least that wide. Enter the limit from centre to centre.
- Select Calculate post marks. Use either the “From start” or “From end” column and keep measuring from that same end. Adding rounded bay lengths one by one can move the final mark.
Worked example: mark five post centres along a 5 m run
Allow 0.1 m at each end of a 5 m run. That leaves 4.8 m between the first and last post centres. With a 1.5 m maximum, the calculator divides it into four equal bays of 1.2 m. Mark the five centres at 0.1, 1.3, 2.5, 3.7 and 4.9 m from the start. The second post, for example, is 1.3 m from the start or 3.7 m from the far end.
Change the rule to a 1.5 m minimum and the same run needs four posts with three 1.6 m bays. A minimum and a maximum give different layouts even when the number you enter is the same.
Post spacing and layout FAQs
How do post centres differ from the clear space between posts?
Post centres locate the middle of each post; the clear space runs from inside face to inside face. Two 100 mm-wide posts at 1,200 mm centres leave 1,100 mm clear between them. Use that face-to-face opening in the railing spindle spacing calculator.
Can I measure the run in metres and mark the positions in millimetres?
Yes. Choose millimetres, centimetres or metres for entry. After calculating, select millimetres or metres for the results. Inches are available for both entry and results, including mixed numbers such as 3 1/2.
Does the calculator tell me the safe span for a fence or railing?
No. It gives geometric set-out marks for the limit you supply. It does not determine structural adequacy, specify post sizes or footings, or check regulatory compliance. Use the span specified for your material, installation and project.
For rails cut between posts, use the linear cutting calculator with the finished cut sizes from your design.
Calculations run in this browser. Enter decimals without thousands separators. Display precision changes the labels, not the layout.
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