About this calculator
Equal spacing for balusters that keeps every gap under the building code’s 100 mm (4") 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
- 3.875 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 wood moves. 3⅞" (98 mm) keeps you under 100 mm.
- Guards are required where the drop is more than 600 mm (2 ft). For a house they must be at least 900 mm (35½") high, or 1070 mm (42") on decks more than 1.8 m (5' 11") above the ground.
- 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 building code adopted in your province before ordering.