🚪

Egress Width Calculator

Reference: NFPA 101 / IBC

🚪 FIRE

Free egress width calculator. Work out required exit door and stair width from occupant load and area using NFPA 101 / IBC capacity factors for safe means of egress design.

Inputs

Results

Was this helpful?

💬 Suggest an improvement

Engineering Intelligence

🛡️ Engineering Alerts

VERIFIED

Run a calculation to evaluate engineering alerts.

📐 DETAILED CALCULATIONS

Governing equation and computation steps will appear here.

📋 ASSUMPTIONS & BASIS

NFPA 101 / IBC

Design criteria, governing codes and assumptions.

ℹ About This Calculator

The width of exit doors, corridors and stairs must be enough to evacuate everyone on the floor within a safe time. This calculator estimates the occupant load from the floor area and use, then applies the code capacity factor (millimetres of width per person) for level components and for stairs to give the minimum required egress width, so you can check door leaves, corridors and staircases against NFPA 101 / IBC.

Occupant load factors and capacity factors come from the adopted life-safety code and vary by occupancy — assembly, business, mercantile, residential and so on. Stairs need more width per person than level components because travel is slower. The calculated width is a minimum; door hardware, handrails and the need for at least two independent exits often govern the final design. Always work to the specific edition of NFPA 101 or IBC adopted for the project.

Egress Width Method (NFPA 101 / IBC)

NFPA 101 / IBC

Step 1 - Occupant load = floor area / occupant load factor for the use (m² per person).
Step 2 - Required width = occupant load x capacity factor (mm per person) - larger for stairs than for level egress.
Step 3 - Compare with the minimum door/corridor/stair widths in the code and take the greater.
Step 4 - Provide at least two remote exits and check that losing one exit still leaves adequate capacity.

Worked Example

A 900 m² business floor with an occupant load factor of 9.3 m²/person gives about 97 occupants. At a level-egress capacity factor of 5 mm/person the required door/corridor width is 97 × 5 ≈ 485 mm, but the code minimum clear door width (typically ≥ 815–900 mm) governs. For stairs at ~7.6 mm/person the width is 97 × 7.6 ≈ 740 mm, again checked against the code minimum stair width.

Means of Egress — Design Notes

Occupant load drives everything

Egress width is only as good as the occupant load behind it. Use the correct load factor for each use within the building and add fixed-seat or posted occupancies where they apply. Mezzanines and accessory spaces contribute to the floor they discharge onto.

Two-exit rule and remoteness

Most occupancies need at least two exits placed remotely so a single fire cannot block both. Capacity is then split between them, and the design is checked with the most demanding exit assumed unavailable.

Beyond width

Clear width is reduced by door hardware, handrails and encroachments, and travel distance, dead-end corridors and discharge arrangements must also comply. Use this tool for the width screen, then complete the full life-safety analysis to code.

Frequently Asked Questions

How is occupant load calculated? +

Divide the floor area by the occupant load factor for the use — for example a denser factor for assembly spaces and a looser one for offices. The result is the number of people the space is assumed to hold for egress design.

Why are stairs wider per person than doors? +

People move more slowly and less steadily on stairs, so codes apply a larger capacity factor (more millimetres per person) to stairs than to level components like doors and corridors.

Does one wide exit satisfy the code? +

No. Codes require at least two remote means of egress for most occupancies, and the design must still work if one exit is blocked, so capacity is shared across independent exits.

What is the minimum door width for egress? +

Codes set an absolute minimum clear width for exit doors regardless of the calculated value; take the larger of the calculated width and the code minimum.

Which code should I use? +

Use the life-safety code adopted for the project location and building type — commonly NFPA 101 or the International Building Code (IBC). Factors differ between editions and occupancies.