Handrail Calculator - Part M & BS 8300 Lengths, Heights & Extensions
Calculate handrail lengths, heights and extensions for stairs and ramps per Approved Document M and BS 8300.
Total horizontal going of stair or ramp
Number of separate flights (between landings)
Total vertical rise from bottom to top
How We Calculate This
This calculator determines handrail lengths, bracket quantities, and compliance with BS 8300:2018 and Approved Document M/K for stairs and ramps.
Slope length calculation
The handrail follows the slope of the stair or ramp. The slope length is calculated using Pythagoras: Slope = √(Going² + Rise²). Extensions are added at top and bottom of each flight.
BS 8300 requirements
- Height (stairs): 900-1000mm from pitch line
- Height (ramps): 900-1100mm from ramp surface
- Extensions: Minimum 300mm beyond top and bottom
- Diameter: 40-45mm circular (50mm max)
- Wall clearance: 50-75mm
- Brackets: At 900-1200mm centres, below rail
Material estimate
A 5% waste allowance is added to the total handrail length for cuts, joins, and off-cuts. Bracket quantities are calculated at 1000mm centres with an end bracket at each termination point.
Frequently Asked Questions
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Last updated: March 2026
All calculations are estimates. Verify with your supplier.