About this calculator
Equal spacing for balusters that keeps every gap under the 4" sphere rule, with the first-centre measurement for marking out.
How it’s calculated
Count = ceil((length − max gap) ÷ (baluster width + max gap)). Actual gap = (length − count × width) ÷ (count + 1).
Worked example
With these inputs:
- Rail length between posts
- 72 in
- Baluster width
- 1.5 in
- Maximum gap
- 4 in
- Number of sections
- 4
the result is:
- Balusters per section
- 13
- On-centre spacing
- 5-1/4"
- First baluster centre from post
- 4-1/2"
- Total balusters
- 52
Tips from the trade
- Set your maximum a little under the limit, because timber moves. 3⅞" or 95 mm is safer.
- Make a spacer block cut to the gap and use it on every baluster.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and local building codes before ordering.