Balustrade Calculator

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. Use our Spindle Spacing Calculator to work out the exact gap and spindle count.

Balusters set out between two newels give one more gap than balusters (gap–baluster–gap–…–gap), so there are n+1 gaps for n balusters. Work out the minimum count: balusters = round up of (length − max gap) ÷ (baluster width + max gap). For a 3m clear run with 32mm balusters and a 99mm max gap: (3,000 − 99) ÷ (32 + 99) = 22.1, round up to 23 balusters. Then the even actual gap is (3,000 − 23 × 32) ÷ (23 + 1) = 2,264 ÷ 24 = 94.3mm — under 100mm and compliant.

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.

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.

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.