How is required exit width calculated under the Ontario Building Code?
Required exit width equals the occupant load multiplied by 6.1 mm per person for doorways, corridors and shallow ramps, or 9.2 mm per person for stairs, and never less than the fixed minimum widths, such as 1 100 mm for most exit stairs.
Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.
Run the calculation per storey and remember that occupant loads converge: stairs pick up load floor by floor in some configurations, and exit capacity cannot decrease along the path of travel. If one exit is lost, the remaining exits often must still carry a share of the load, so avoid designing exactly to minimums. Doors count at their clear width, and a leaf under about 610 mm clear contributes nothing.
Count the people on the floor, then give each person a small slice of doorway or stair width, a bit more for stairs since people move slower going down. Add it up and the exits must be at least that wide.
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This page is provided for general information. Building code requirements depend on your specific project, occupancy and municipality, and code editions change. Always verify requirements against the current Ontario Building Code and confirm with your local building department.