Handrail Calculator - Part M & BS 8300 Lengths, Heights & Extensions

For both stairs and ramps, the top handrail should be between 900mm and 1000mm high, measured vertically from the pitch line of the steps or the ramp surface (the pitch line is the imaginary line connecting stair nosings). At landings the height range is 900mm to 1100mm. Where there is full-height structural guarding, Approved Document M §1.37(b) also requires a second, lower handrail at 600mm for children and people of short stature. Both Approved Document M Volume 2 and BS 8300-2:2018 give the 900-1000mm range, and it applies to both sides of the stair or ramp.

BS 8300 requires handrails to extend at least 300mm horizontally beyond the top and bottom of each flight. At the top of stairs, the extension continues at the same height horizontally. At the bottom, it extends 300mm horizontally from the bottom nosing. These extensions help users maintain grip as they transition to level ground and provide a tactile warning that the stair or ramp has ended.

Approved Document M §1.37(h) permits a circular handrail of 32-50mm diameter. BS 8300-2:2018 narrows this to a 40-50mm circular cross-section, with 40-45mm being preferred for the best grip, so most accessible installations aim for 40-45mm. A non-circular profile of 50mm wide and 39mm deep with rounded edges (minimum 15mm radius) is also acceptable. The rail must be smooth and warm to touch, so metal handrails should have a PVC or nylon coating to avoid being cold in winter.

Approved Document M §1.37(j) requires a clearance of between 50mm and 75mm between the handrail and any adjacent wall surface (measured to the wall-facing surface of the rail). BS 8300-2:2018 recommends the tighter 50mm to 60mm band for better accessibility, so aiming for 50-60mm satisfies both. The 50mm minimum lets fingers wrap the rail; the maximum stops a child becoming trapped between the rail and wall. There must also be at least 50mm between a cranked support and the underside of the rail, and brackets must not obstruct the continuous hand grip.

Building Regulations Approved Document K requires a handrail on at least one side for stairs less than 1000mm wide, and on both sides for stairs 1000mm or wider. For accessible (Part M) stepped and ramped access, Approved Document M expects a continuous handrail on each side of a flight and its landings. BS 8300 likewise recommends handrails on both sides regardless of width for maximum accessibility. For ramps, AD M expects a handrail on both sides, and once the rise exceeds 300mm (= 2 × 150mm steps) it also expects clearly sign-posted steps as an alternative to the ramp.