IBC egress width requirements

The Quick Answer

Per IBC Section 1005.3.1, required egress width = occupant load × 0.3" (for stairways, sprinklered building) or × 0.2" (for corridors, doors, and other level components). If the building is not fully sprinklered, the factors increase to 0.5" and 0.3" respectively (IBC 1005.3.2). Minimum absolute widths still apply even if the calculation is smaller.

Minimum Width Floors (IBC 1011.2, 1020.2, 1010.1.1)

Regardless of calculated width, minimums apply:

• Stairways: 44" minimum clear width (IBC 1011.2). 36" allowed for occupant load <50 or certain dwelling unit stairs
• Corridors: 44" minimum in most occupancies (IBC 1020.2). 36" for serving <50 occupants. 72" for healthcare with bed movement
• Exit doors: 32" minimum clear width (IBC 1010.1.1), measured between face of door and stop when opened 90 degrees
• Accessible routes: 36" minimum (IBC/ADA 403.5.1)

The 50% Rule (IBC 1005.5)

When two or more exits are provided, the total egress capacity must be arranged so that the loss of one exit does not leave the remaining exits with less than 50% of the required capacity. In practice, no single exit can serve more than 50% of the occupant load in a two-exit configuration.

For a 300-occupant floor with three exits, each exit needs egress capacity for 150 occupants (50% × 300), not 100 (300 ÷ 3). Drawing review should verify the exit assignment in the occupant-load schedule.

Convergence (IBC 1005.6)

When egress paths converge, such as where upstairs occupants enter a stair already carrying downstairs occupants, the egress width must account for the combined load. The stair width from that level down must be the greater of either floor's requirement plus the convergence load.

This applies at stair merging, corridor junctions, and at the level-of-exit-discharge. Many code reviewers miss this because the calculation is not done floor-by-floor in a naive schedule.

Travel Distance and Common Path (IBC 1006, 1017)

Egress width is paired with travel distance:

• Common path of egress travel (single direction before two paths available): 75'–100' typical by occupancy
• Travel distance to an exit: 200'–300' typical, longer with sprinklers
• Dead-end corridor length: 20' typical, 50' sprinklered (by occupancy)

These numbers drive exit placement and affect overall egress calculation as much as width does. Review both together on the life safety plan.

Example Calculation

Classroom floor in a sprinklered Group E school, occupant load 450:

• Stair width required: 450 × 0.2 = 90" total
• With three stairs, each sized for 50% × 450 = 225 occupants: 225 × 0.2 = 45" (use 48" to exceed minimum)
• Corridor width to each stair: 225 × 0.2 = 45" (use 60" corridor for school typical)
• Exit door width at stair discharge: 32" clear minimum; check capacity: 32" ÷ 0.2 = 160 occupants per door

For assembly occupancies, start with our occupant load calculation.