How Many Spindles Do I Need?
Quick Answer
Gap must be <100mm (UK Building Regs) — typically 1 spindle per 100–120mm
Based on: 32mm or 41mm square spindles, with gaps no greater than 99mm. A 3m balustrade typically needs 25–30 spindles.
How We Calculated This
The key rule is that a 100mm sphere must not pass through any gap in the balustrade (Approved Document K of UK Building Regulations):
- Balustrade length: 3m (3000mm)
- Spindle width: 32mm (standard square spindle)
- Maximum gap: 99mm
- Spindle + gap = 32 + 99 = 131mm per module
- Spindles: 3000 ÷ 131 = ~23 spindles
- For even spacing with slightly smaller gaps: 25–28 spindles is typical
Common Spindle Sizes
- 32 × 32mm: Standard square spindle (most common)
- 41 × 41mm: Larger square spindle (more substantial look)
- Turned spindles: Decorative, diameter varies from 32–55mm. Use the narrowest point for gap calculation.
- Metal spindles: 12–16mm diameter, more spindles needed due to narrower width
UK Building Regulations (Approved Document K)
- Maximum gap: 99mm (a 100mm sphere must not pass through)
- Minimum handrail height: 900mm for stairs, 1100mm for landings and balconies
- Guarding required: Where there is a drop of 600mm or more
- No climbable features: Horizontal rails below 600mm that could allow climbing are not permitted
Spindle Spacing Formula
To calculate even spacing: divide the balustrade length by the desired module (spindle width + gap). Adjust the gap slightly to get a whole number of spindles. The gap must always be less than 100mm.
Tips
Use a spacer jig cut to the correct gap size for consistent spacing. Fix spindles with dowels, screws, or dedicated spindle fixings into the handrail and base rail/string. On rake sections (stairs), spindles should be cut at an angle at top and bottom to sit plumb. Always check with a 100mm test sphere after installation.