| Primary value | 300 mm |
| Applies to | Schools · Hospitals · Offices · Cinemas, halls · Hotels |
| Exceptions | Residential individual house → 250 mm allowed |
| Measured as | Horizontal tread depth, riser to nosing. |
| Source | NBC 2016 — Part 4, Clause 4.4.2 ✓ Verified |
300 mm gives the full foot plus some margin to land securely — critical for crowd flow, where descending users can't carefully place each step. The wider tread also slows descent in emergencies, reducing fall risk.
300 mm is the universal minimum for commercial/public stairs. Hotel and theatre stairs sometimes use 320-350 mm for a sense of generosity.