Calculate Spindle Spacing

Number of Spindles Required

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Spacing Between Spindles

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End Gaps

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Spacing Layout

UK Building Regulations for Spindle Spacing

In the United Kingdom, building regulations are strict about spindle spacing to prevent accidents, particularly involving children. The key regulation states that no gap between spindles should allow a 100mm sphere to pass through. This means the maximum spacing between any part of adjacent spindles must be 99mm or less.

Safety Requirement

The 100mm sphere test is designed to prevent children’s heads from becoming trapped between spindles. This applies to all balustrades on stairs, landings, and elevated surfaces such as decks and balconies.

Stair Spindles

For staircases, spindles must be installed between the handrail and base rail, maintaining the 99mm maximum gap rule throughout the entire flight.

Landing Balustrades

On landings and horizontal surfaces, the same 99mm rule applies, with spindles providing a barrier at least 900mm high for residential properties.

External Decking

Deck balustrades follow identical spacing rules, with additional weather resistance considerations for outdoor installations.

How to Calculate Spindle Spacing

Method 1: Even Spacing Throughout

This method creates uniform gaps between all spindles, including the end gaps:

Spacing = (Total Length - (Number of Spindles × Spindle Width)) ÷ (Number of Spindles + 1)
  1. Measure the total railing length between posts or walls
  2. Determine the number of spindles needed using the maximum spacing rule
  3. Calculate total spindle width by multiplying spindle width by quantity
  4. Subtract total spindle width from railing length to find available space
  5. Divide available space by number of gaps (spindles + 1)

Method 2: Centred with Balanced End Gaps

This method centres the spindles with equal end gaps, creating a more balanced appearance:

  1. Calculate the number of spindles as above
  2. Space spindles at the maximum allowed distance
  3. Calculate remaining space and divide equally between the two end gaps
  4. Position first and last spindles with these balanced end gaps

Common Spindle Sizes and Spacing

32mm Wood Spindles

Quick calculation: Divide railing length by 112mm
Typical spacing: 80-99mm between spindles
Best for: Modern, sleek designs

35mm Wood Spindles

Quick calculation: Divide railing length by 115mm
Typical spacing: 80-99mm between spindles
Best for: Standard residential staircases

41mm Wood Spindles

Quick calculation: Divide railing length by 121mm
Typical spacing: 80-99mm between spindles
Best for: Traditional, substantial appearance

Metal Spindles

Quick calculation: Divide railing length by 105mm
Typical spacing: 85-99mm between spindles
Best for: Contemporary designs, outdoor use

Installation Guidelines

Measuring Your Railing

  • Measure the inside distance between newel posts or walls
  • For staircases, measure the horizontal “going” distance, not the sloped length
  • Account for any existing posts or obstacles in your measurement
  • Double-check measurements before ordering materials

Marking Spindle Positions

  • Start by marking the centre line of your railing
  • Use the calculated spacing to mark each spindle position
  • Check that all gaps meet the 99mm maximum requirement
  • Mark both the top handrail and bottom rail positions

Special Considerations

  • Turned spindles: Measure at the narrowest point to maintain compliance
  • Cut string staircases: May require alternating spindle lengths
  • Curved staircases: Calculate spacing along the curve, not straight-line distance
  • Glass panels: Different spacing rules may apply – check local regulations

Frequently Asked Questions

Why is 99mm the maximum spacing?

This measurement prevents a 100mm sphere (approximately the size of a young child’s head) from passing through, reducing the risk of entrapment and injury.

Can I space spindles further apart for a more open look?

No, building regulations require compliance with the 99mm maximum spacing for safety reasons. This applies to all residential and commercial properties.

Do I need building approval for spindle installation?

New staircases and balustrades typically require building control approval. Replacement spindles on existing compliant structures may not need approval, but check with your local authority.

What if my calculation gives a fraction of a spindle?

Always round down to the nearest whole number of spindles. This ensures you don’t exceed the maximum spacing allowed by regulations.

How do I handle corners and turns?

Measure each straight section separately and calculate spindle spacing for each section independently. Corner posts typically separate different sections.

Can I mix different spindle sizes?

Yes, but ensure that the spacing between any adjacent spindles (regardless of size) doesn’t exceed 99mm at any point along their length.