# Egress Width Calculator

Occupants times the per-100-persons index gives total width and exit count.

- Page: https://jianzhujisuan.com/en/egress-width
- Category: Code Lookup (https://jianzhujisuan.com/en/c/code-lookup)
- Chinese version: https://jianzhujisuan.com/zh/egress-width.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Occupant load 500 persons, Storey Ground to 2nd storey, Fire resistance rating Grade I or II, Crowded occupancy General public building): **Required total egress width 3.25 m**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Occupant load | number | 500 | persons |  |
| Storey | select | Ground to 2nd storey | — |  |
| Fire resistance rating | select | Grade I or II | — |  |
| Crowded occupancy | select | General public building | — |  |

## Formula

- **Total width**: B = occupants ÷ 100 × index
- **Index**: ground-2nd 0.65/0.75/1.00; 3rd 0.75/1.00; 4th+ 1.00/1.25
- **Basement**: 0.75 at ≤10 m depth, 1.00 beyond; crowded rooms min 1.00
- **Min per exit**: 0.90 m general, 1.40 m crowded
- **Exit count**: at least two per compartment

## Worked example

3rd storey, grade II, 500 people: index 0.75 gives 3.75 m total; at 0.90 m minimum per exit that divides into 5 exits averaging 0.75 m, which is below the minimum, so 5 exits of at least 0.90 m each (4.5 m total) is what gets built.

## Questions

### How is the occupant load calculated?

Not by dividing floor area arbitrarily - use the code density figures: retail halls around 0.5-0.85 persons/m² depending on storey and size, entertainment venues 0.5 persons/m², offices 4-8 m² per person, classrooms 1.0-1.2 m² per person. Getting this wrong is one of the most common reasons fire reviews are returned.

### Why does a higher storey need a wider index?

Because egress is longer and depends on stairs, which become the bottleneck in a fire. A larger width per person effectively gives the stairs more capacity - hence 1.00 m per 100 persons at the 4th storey and above versus 0.65 at the lower floors.

### The total is 3.75 m - can I just use four 1 m doors?

The total works but each door must also meet the minimum clear width (0.90 m, or 1.40 m in crowded occupancies), and the travel distance from the worst point must still comply. Remember clear width excludes the frame and the open leaf, so a 1 m opening often gives about 0.9 m of usable width.

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