What is the maximum gap between balusters?

Under Building Regulations Part K, the maximum gap between balusters (spindles) must be less than 100mm (a 100mm sphere must not pass through). In practice this means a maximum clear gap of 99mm. This applies to staircase balustrades, landing balustrades, and balcony railings in all buildings.

How do I calculate the number of balusters needed?

Divide the total balustrade length by the pitch (baluster width + gap). For 32mm balusters with 100mm max gaps: pitch = 132mm. For a 3m run: 3,000 ÷ 132 = 22.7, round up to 23 balusters. Then recalculate the actual gap: 3,000 ÷ 23 - 32 = 98.4mm gap — which is under 100mm and compliant.

What height should a newel post be?

Newel posts typically extend from the floor to 1100-1300mm above the string. The handrail connects at 900-1000mm measured from the pitch line (stairs) or floor (landings). For external balconies, the minimum guarding height is 1100mm. Newels should extend above the handrail by 50-100mm for a traditional cap detail. Landing newels are measured from the landing floor.

Do I need a base rail for a balustrade?

A base rail (bottom rail) helps with even baluster spacing and provides a clean bottom edge. For traditional balustrades, balusters are pinned into both the handrail and base rail. Some systems use spacer blocks between balusters instead. The base rail should be fixed to the string or floor with concealed brackets.

What handrail height is required on stairs?

Building Regulations Part K requires handrails at 900-1000mm measured vertically from the pitch line (the line connecting stair nosings). On internal landings in dwellings, the guarding height is 900mm minimum. On external balconies, it is 1100mm minimum. At least one handrail is required for stairs under 1m wide; both sides for wider stairs.

TradeCalculator.co.uk

Balustrade Calculator

Calculate baluster count for 99mm max gap compliance (Part K sphere test), handrail length, newel height and base rail.

Total Balustrade Length

Total run of balustrade

Baluster ProfileWidth affects gap spacing

Number of Newel Posts

Top and bottom of each flight

Newel Height

Full height from floor

Price Per Baluster (optional)

Price Per Newel (optional)

Price Per Metre Handrail (optional)

How We Calculate This

This calculator determines the number of balusters to achieve a maximum 100mm gap (Part K compliance), plus handrail length, base rail and newel post quantities.

The formula

Balusters = Length ÷ (Baluster width + Max gap)
Actual gap = (Length ÷ Balusters) - Baluster width
Handrail length = Total balustrade run
Must satisfy: Gap < 100mm (100mm sphere must not pass through)

Part K requirements

99mm max clear gap (100mm sphere must not pass through)
Handrail 900-1000mm on stairs and internal landings, 1100mm on external balconies
Balustrade must resist 0.36 kN/m horizontal loading
No climbable features below 600mm height