About this calculator
Equal spacing for balusters that keeps every gap under the NCC 125 mm 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
- 1800 mm
- Baluster width
- 42 mm
- Maximum gap
- 120 mm
- Number of sections
- 4
the result is:
- Balusters per section
- 11
- On-centre spacing
- 154 mm
- First baluster centre from post
- 133 mm
- Total balusters
- 44
Tips from the trade
- Set your maximum a little under the limit, because timber moves. 120 mm is safer.
- Balustrades must be at least 1 m high on decks and landings where the fall is more than 1 m, and 865 mm above stair nosings. Where the fall is more than 4 m, avoid horizontal rails that children can climb.
- 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 the NCC and Australian Standards before ordering.