Inputs
White themeSpan & margins
in
Measured straight along the rail line.
in
in
Baluster
in
Stair guard often allows 4⅜ in maximum clear gap.
Strategy
in
Switch to “Stair guard” to auto-set 4⅜″ (111 mm) suggestion.
in
Formula used
Let S be usable span = span − left − right, w baluster width, g clear gap, t center spacing, and N baluster count.
- Equal end gaps: gaps are equal everywhere, including ends: S = N·w + (N+1)·g. With limit g ≤ gmax, choose N = ceil((S − gmax)/(w + gmax)), then compute g = (S − N·w)/(N+1) and t = w + g.
- Half-spacing at ends: end gaps are half of interior gaps: S = N·w + N·g. With g ≤ gmax, choose N = ceil(S/(w + gmax)), then g = (S − N·w)/N, end gaps = g/2, centers t = w + g.
- Fixed centers: choose t; maximum N satisfying w + (N−1)·t ≤ S is N = floor((S − w)/t) + 1. Interior gap g = t − w, end gaps equal: (S − (w + (N−1)·t))/2.
- Fixed count: with chosen N, compute as above for the selected end treatment.
Local codes vary; many use 4″ maximum clear gap, and 4⅜″ on stair guards. Always verify with your authority.
Results
inBaluster count
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Interior clear gap
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Center spacing
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End gap
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Usable span
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Mode
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Baluster layout
| # | Center from left | Left edge | Right edge | Interior gap to next |
|---|
Positions measured from the inner face of the left newel + left margin.
Example data table
Sample scenarios. Change units to see converted values; results populate live.
| Scenario | Span | Margins L/R | Baluster | Mode | Limit/Setting | N | Gap | Centers |
|---|
How to use
- Select your units and profile, then enter the clear span.
- Set left/right margins if you keep balusters away from newels.
- Enter baluster width/diameter. Pick your strategy: auto, centers, or count.
- If using auto, choose end treatment and confirm the maximum clear gap.
- Press Calculate. Review the summary and layout table below.
- Export CSV for takeoffs or PDF for submittals and quotes.
Tip: “Half-spacing at ends” centers the pattern, giving half a bay at each end.
FAQs
Clear gap is the empty space between baluster edges. Center spacing equals baluster width plus the clear gap, measured from center to center.
Commonly 4″ for level guards and 4⅜″ for stair guards, but requirements vary by jurisdiction. Always confirm with the local authority having jurisdiction.
Choose equal end gaps (equal everywhere) or half-spacing at ends, which centers the pattern and leaves half a bay at both ends.
Yes. Use “Fixed baluster count”. The calculator will compute the resulting gap and end gaps so you can verify compliance.
For width-based spacing, treat round diameter as the width. The tool reports edge-to-edge clear gaps; tangent clearance for round and square is equivalent for this purpose.
Yes. Balusters are vertical; span is measured along the rail. For stair guards, use the 4⅜″ suggestion, but confirm final details with your code official.