How Many Balustrade Spindles Do I Need?
Quick Answer
Maximum 100mm gap between spindles (Building Regs)
Based on: Approved Document K. Typically 110–120mm centres. A 3m balustrade needs ~25–27 spindles.
The Building Regulations Rule
Approved Document K (England) requires that a 100mm sphere cannot pass through any gap in a balustrade or guarding. This means the gap between spindles must be less than 100mm.
How to Calculate
For a typical 32mm square or turned spindle:
- Maximum gap: 99mm (to stay under 100mm)
- Centre-to-centre spacing: 32 + 99 = 131mm maximum
- In practice, most joiners use 110–120mm centres for a better look
- Spindles per metre: 1,000 ÷ 115 = approximately 8.7, say 9
Example — 3m landing balustrade at 115mm centres:
- 3,000 ÷ 115 = 26.1, round up to 27 spindles
Staircase Spindles
On a staircase, spindles are fitted to treads (typically 2 per tread). The number of spindles = number of open treads × 2. The rake angle means gaps can change — always check with a 100mm sphere test.
Standard Spindle Sizes
- 32mm square: Most common for modern staircases
- 41mm turned: Traditional profile
- 900mm long: Standard for landings (cut to suit for raked sections)
Last updated: April 2026. Always verify compliance with Building Regulations Approved Document K. A 100mm sphere test is the definitive check.