Exit Width Calculator: Egress Width, Number of Exits and Travel Distance
The exit width needed for the number of people, whether your exits provide it, and the travel distance against the limit.
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How this calculator works
In an emergency the people in a building must be able to leave quickly. The first check is arithmetic: the number of people times the exit width the code asks for each person gives the total width needed, and the exits provided must add up to at least that.
Good design also asks what happens if one exit is blocked by the fire. The calculator shows the width left with one exit out of use, how many exits of that width are needed at the least, and how the furthest travel distance compares with the limit.
The width for each person and the travel distance limit depend on the building class and use, so they are inputs from the National Construction Code or a fire engineering report. This is a check of the arithmetic only, and a fire engineer or building certifier decides the design.
Formulas used
- W_{req} = N \times w_{pp}
- W_1 = (k-1)\,w
- k_{min} = \lceil W_{req}/w \rceil
Worked example
With the default numbers in the calculator above:
- Total exit width needed: 1000.00 mm
- Exit width provided: 2000.00 mm
- Width left with one exit out of use: 1000.00 mm
- Exits needed at this width: 1
- Travel distance margin: 10.00 m
Change the numbers in the calculator to see the full working, every step, for your own case.
A second worked example
A different case, with these numbers: Number of people who may need to leave 450.
- Total exit width needed: 2250.00 mm
- Exit width provided: 2000.00 mm
- Width left with one exit out of use: 1000.00 mm
- Exits needed at this width: 3
- Travel distance margin: 10.00 m
Common questions
What width per person do I use?
The one given in the National Construction Code or your fire engineering report for the class and use of the building. The default is an example only.
Why check with one exit out of use?
A fire can block an exit. Many designs make sure the remaining exits can still handle the people.
Does this approve my egress design?
No. Exit position and spread, doors, stairs, signs and lighting have their own rules, and a certifier approves the design.
Related calculators
Got a question about this? Ask an engineering question and get a plain-language answer with references.
Further reading: National Construction Code (Building Code of Australia), egress provisions; AS 1670.4 (emergency warning and intercom, licensed); your building certifier or fire safety engineer.
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