Work out exit capacity instantly with clear inputs, formula shown and shareable results.
The unit of exit width convention treats a 550 mm module as passing a fixed number of occupants, historically 100 for a level exit and 60 for stairs. Codes also require the remaining exits to serve the full occupant load with the largest exit discounted, since a fire may block the exit nearest to it.
Exit capacity
Capacity = (clear width / 550) x occupants per unit x number of exits
Redundancy
Recalculate with the largest exit discounted
Preliminary estimate only. Exit capacity and redundancy requirements must be taken from the fire and building code adopted locally.
Capacity = (clear width / 550) x occupants per unit x number of exits. The unit of exit width convention treats a 550 mm module as passing a fixed number of occupants, historically 100 for a level exit and 60 for stairs.
Many modern codes have moved to millimetres per person, but the underlying idea is the same and the unit method remains common in building regulations and fire safety guidance.
This calculator takes 3 inputs: Clear width per exit, Occupants per unit of width, Number of exits. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.