What this tool does
Computes how many balusters you need and the resulting actual gap, from the total rail length, baluster width, and target gap, with equal gaps at both ends.
How to use it
- Enter the total rail length in centimetres.
- Enter one baluster’s width.
- Enter the target gap.
- Run it for the baluster count and the actual gap.
Worked example
A 200 cm rail with 4 cm balusters and a 10 cm target gap needs 14 balusters, giving an actual gap of 9.6 cm.
Calculation method
Baluster count
max(0,ceil((length-gap)/(width+gap)))Equal gap
(length-max(0,ceil((length-gap)/(width+gap)))*width)/(max(0,ceil((length-gap)/(width+gap)))+1)Frequently asked questions
- Why is the actual gap narrower than my target?
- The count is rounded up, which adds one baluster and splits the remaining space into more gaps, so each gap narrows. Narrower is the safer direction.
- How do I choose a target gap?
- Local building codes often set a maximum permitted gap. This tool does not evaluate code, so check the rules that apply and set your target accordingly.
What this tool does not cover
Even spacing along a straight rail. Stair pitch, newel positions, corners, and code compliance are not evaluated.