Spindle spacing calculator: spindles, gaps and marking out
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
Worked example
| You enter | Value |
|---|---|
| Level or raked? | Level (landing or deck) |
| Length between newels | 2,000 mm |
| Spindle width | 41 mm |
| Largest gap allowed | 99 mm |
You need 14 spindles with 95.1 mm gaps
- Within the guidance Gap between spindles (100 mm sphere must not pass): 0.095 m England: Approved Document K: guarding, 100 mm sphere (paragraph to be cited). Check with the source
| Result | Value |
|---|---|
| Spindles | 14 |
| Gap between spindles (horizontal) | 95.07 mm |
| Spindle centres along the rail | 136.1 mm |
Marking out: centre of each spindle from the left newel, along the rail
- Spindle 1: 115.6 mm
- Spindle 2: 251.6 mm
- Spindle 3: 387.7 mm
- Spindle 4: 523.8 mm
- Spindle 5: 659.8 mm
- Spindle 6: 795.9 mm
- Spindle 7: 932 mm
- Spindle 8: 1,068 mm
- Spindle 9: 1,204.1 mm
- Spindle 10: 1,340.2 mm
- Spindle 11: 1,476.2 mm
- Spindle 12: 1,612.3 mm
- Spindle 13: 1,748.4 mm
- Spindle 14: 1,884.4 mm
Show the working
- Spindles: (2,000 − 99) ÷ (41 + 99) = 13.58, rounded up = 14
- Gap: (2,000 − 14 × 41) ÷ (14 + 1) = 95.07 mm
- Centres: (95.07 + 41) = 136.1 mm; first centre 115.6 mm from the newel
How it works
- Level: n = (L − g) ÷ (w + g), rounded up; gap = (L − n × w) ÷ (n + 1), where L = length between newels, w = spindle width, g = largest gap allowed
- Raked: the horizontal length is L × cos(rake angle); n and the horizontal gap use that length; centres along the rail = (gap + w) ÷ cos(rake angle)
- First centre from the newel = gap + w ÷ 2 (along the rail when raked)
The 100 mm sphere rule applies to the gap between spindles and under the bottom rail; measure the finished gap after fitting.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Largest gap allowed | 99 mm | Regulation or HSE figure Approved Document K: guarding, a 100 mm sphere must not pass (paragraph to be cited) Not yet checked against the source | gov.uk (checked 19 October 2026) brief v2 F1 (99 mm default from the 100 mm sphere rule). Researcher to cite the paragraph; Wales has its own Approved Document K. |
Regulations and standards
- Approved Document K: guarding, a 100 mm sphere must not pass between spindles (paragraph to be cited)
Explained: Approved Document K (stairs and guarding).
The check uses Approved Document K for England. Wales has its own Approved Document K; Scotland and Northern Ireland have their own guidance.