How this egress stair capacity calculator works
Clear width is the total stair width minus the parts that cannot be walked on, such as handrail projections and balustrades. This page works out the clear width first, divides it by the width per person you enter to get the capacity of one stair, and multiplies by the number of stairs. Enter the occupant load of the floor and it also returns the shortfall and the extra clear width needed.
The formula applied is capacity = floor(clear width / width per person) x number of stairs. Because it counts people who actually fit, the division rounds down, while the extra width needed to close a shortfall is rounded up. The deduction and the width per person were not confirmed from an authoritative source. Per-person egress width factors vary with occupancy and with the code applied, and secondary sources did not confirm a single value, so no figure is supplied here; you enter the value from the code you work to. Figures reflect October 2026.
Sizing the stair width from an occupant load, riser and tread dimensions, landing sizes, travel distance and the required number of exits are not covered. This calculator is for reference and does not replace design. Review by a qualified engineer is required.
Frequently asked questions
Enter the per-person width taken from the code or design guide you are working to. No verified conversion factor was confirmed from an authoritative source, so this page does not supply one.
Enter the total of handrail projections, balustrades and wall projections that cannot be counted as walking width. What must be deducted differs between codes, so follow the one you apply.
The page assumes several stairs of the same clear width and simply multiplies. If each stair has a different width, calculate them one at a time and add the results.