Exit Capacity Calculator

Work out exit capacity instantly with clear inputs, formula shown and shareable results.

About Exit Capacity Calculator

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.

Formulas

Exit capacity

Capacity = (clear width / 550) x occupants per unit x number of exits

Redundancy

Recalculate with the largest exit discounted

Worked example

With the default values below, Exit Capacity Calculator returns Total exit capacity of 655. Change any input above and every figure here is recalculated in your browser.

Inputs used

Clear width per exitminimum 100 mm: 1,800 mm
Occupants per unit of widthminimum 1 people per 550 mm: 100 people per 550 mm
Number of exitsminimum 1: 2

Results

Total exit capacity: 655 people
Capacity per exit: 327 people
Units of exit width per exit: 3.273
Capacity with the largest exit discounted: 327 people

Step by step

1Values used
2Exit capacity
3Redundancy
4Total exit capacity= 655 people
5Capacity per exit= 327 people
6Units of exit width per exit= 3.273
7Capacity with the largest exit discounted= 327 people

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Preliminary estimate only. Exit capacity and redundancy requirements must be taken from the fire and building code adopted locally.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Exit capacity and redundancy requirements must be taken from the fire and building code adopted locally.

Frequently Asked Questions

How is the Exit Capacity figure worked out?

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.

Is the unit width method still used?

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.

What values do I need to enter?

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.