How the numbers fit together
A straight run has one gap at each post and one between each pair of balusters. Choose the smallest whole count that keeps every gap at or below G, with at least one baluster. Round the count up, then recalculate the gap.
- Minimum baluster count
- N = max(1, ⌈(L − G)/(B + G)⌉)
- Equal clear gap
- g = (L − N × B)/(N + 1)
- Center-to-center pitch
- p = B + g · M = N + 1
- L · Clear opening between posts
- 2000 mm
- B · Actual baluster width
- 40 mm
- G · Chosen maximum clear gap
- 100 mm
- N · Minimum baluster count
- 14
- M · Number of gaps, including ends
- 15
- g · Equal clear gap
- 96 mm
- p · Center-to-center pitch
- 136 mm
14 × 40 + 15 × 96 = 2000 mm
Use actual width along the row, or diameter for round balusters. All dimensions describe a horizontal straight run. A sloping rail length, tapered balusters and other openings need separate geometry checks.
G is your chosen maximum, not a universal building-code limit. The example uses 100 mm; verify local requirements and the finished guard, including sphere tests, before fabrication.
In the app · English
Tools → Baluster spacing
Mode: Balusters between posts / Face-mounted balusters.
For a row of equal-width balusters. Measure the run using the end condition of the selected mode; the same length produces different counts in the two modes.
- Run length
- Straight run: clear opening between the supports. Attached run: overall length from the outside of the first baluster to the outside of the last.
- Width and maximum gap
- Actual baluster width along the run, and the largest permitted clear opening chosen for this job.
Straight run leaves equal gaps at both ends: n balusters make n + 1 gaps. Attached run puts a baluster at each boundary: n balusters make n − 1 gaps.
Automatic count finds a gap no larger than your maximum. The count controls can add balusters within the valid range; spacing is recalculated.
- Baluster count, clear gap and centre-to-centre pitch.
- A numbered table of leading-edge and centre positions from the same start datum.
The same dimensions, two different end conditions. Values are rounded to 0.001 mm here, not a claim of site measuring accuracy.
| Quantity | Value |
|---|---|
| Run; baluster width; maximum gap | 3000 mm; 40 mm; 100 mm |
| Straight: count; gap; centres | 21; 98.182 mm; 138.182 mm |
| Attached: count; gap; centres | 23; 94.545 mm; 134.545 mm |
Straight: gap = (run − n × width)/(n + 1). Attached: gap = (run − n × width)/(n − 1). Centre pitch = gap + width. Start straight-run leading edges at one gap; start the attached row at zero.
Use metric or imperial dimensions consistently. The maximum gap is your input, not a code-compliance approval. Check requirements for the actual guard or stair before fabrication.
The model is a one-dimensional row. It does not transform a sloping rail measurement into a horizontal clear opening or account for changing baluster widths.
Should I mark centres or edges?
Both are listed. Pick one column and keep the same reference for the entire run.
Why does attached mode need more pieces?
There are no end gaps to share the remaining space; the two boundary pieces are included in the total count.
- Should I mark centres or edges?
- Both are listed. Pick one column and keep the same reference for the entire run.
- Why does attached mode need more pieces?
- There are no end gaps to share the remaining space; the two boundary pieces are included in the total count.
Measurements, units and material terms
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