How do you calculate egress width?

Multiply the occupant load served by the capacity factor, then compare the result with the minimum width for that component and use the larger. Example: 120 people on a stairway need 120 × 0.3 = 36 in of capacity width, but the IBC stair minimum is 44 in, so 44 in governs. 300 people through doors need 300 × 0.2 = 60 in, for example two doors with 32 in of clear width each (64 in).

Which IBC provisions does this calculator use?

IBC 2024 Section 1005.1 (capacity and minimum width, use the larger), 1005.3.1 stairways, 1005.3.2 other components, 1005.5 distribution, 1010.1.1 door clear width, 1011.2 stair width, Table 1020.3 corridor width and 1012.5.1 ramp width. It is a screening tool, not a complete compliance determination.

When may I use the reduced capacity factor?

Under IBC 1005.3.1 and 1005.3.2 Exception 1 the factors drop to 0.2 in per occupant for stairways and 0.15 in for other components in buildings with an automatic sprinkler system (903.3.1.1 or 903.3.1.2) and an emergency voice/alarm communication system (907.5.2.2). The reduction does not apply to Group H or I-2. NFPA 101 has no equivalent general reduction.

How many people can a 44-inch stair serve?

146 occupants at the standard 0.3 in factor (44 ÷ 0.3 = 146.7, rounded down) or 220 with the 0.2 in sprinklered factor. A 36-inch stair, allowed only where it serves fewer than 50 people, serves 120 or 180. The capacity table on this page lists common widths.

Do I add the occupant loads of all floors for a stairway?

No. Under IBC 1005.3.1 stairway capacity is based on the occupant load of each story considered individually, so a stair serving four floors of 150 people each needs capacity for 150, not 600. Where egress from an upper and a lower story converges at an intermediate level, the capacity from that point must be at least the sum of the two (IBC 1005.6).

What is the 50 percent rule for exits?

IBC 1005.5 requires that losing any one exit does not reduce the available capacity or width to less than 50% of what is required. With two equal exits this is met automatically; it matters when one exit is much larger than the others, for example a 72 in door and a 32 in door. Enter existing widths to test it.

What is the minimum corridor width under the IBC?

Table 1020.3 sets 44 in in general, 36 in where the occupant load is under 50 or within a dwelling unit, 72 in in Group E corridors serving 100 or more, 72 in where stretchers serve outpatient care and 96 in in Group I-2 areas used for bed movement. The required width is the larger of this and the capacity width.

How do NFPA 101 capacity factors differ from the IBC?

NFPA 101 Table 7.3.3.1 uses 0.3 in per person for stairs and 0.2 in for level components and ramps in most occupancies, like the IBC, but 0.4 and 0.2 in board and care, 0.6 and 0.5 in nonsprinklered health care, and 0.7 and 0.4 in high-hazard contents areas. It has no general sprinkler reduction to 0.2 and 0.15.

How do I calculate the egress capacity of a door?

Divide the clear width by the capacity factor and round down. A door with 32 in of clear width serves 32 ÷ 0.2 = 160 occupants with the standard factor, or 213 with the reduced 0.15 factor where every condition for it is met. A standard 36 in door leaf usually gives about 32 to 34 in of clear width once the door thickness and stop are subtracted.

Does the result prove code compliance?

No. Exit count, remoteness, travel distance, accessibility, hardware, encroachment, local amendments and the edition your jurisdiction has adopted remain outside this calculator. Confirm the design with the authority having jurisdiction.

Egress Width Calculator

Get the required egress width from the occupant load (the larger of capacity width and the code minimum), split it across exits, or check how many people existing doors and stairs can serve.

Required egress width is the larger of two checks: capacity width (occupant load × 0.3 in per person for stairways, 0.2 in for doors, corridors and ramps, IBC 1005.3) and the dimensional minimum for the component (44 in stair, 32 in clear door, 44 in corridor in most occupancies).

Egress Inputs

Occupant load served (people)

Stairways: the largest single story served, not the sum of all floors.

Code basis

Component

Capacity factor eligibilityStandard factorReduced: qualifying sprinkler and EVACS; not Group H or I-2

Number of exits sharing the load

Existing clear widths (optional, comma separated)

Enter the occupant load to calculate the required width.

Screening only

Exit count, remoteness, travel distance, accessibility, hardware, door-swing encroachment and local amendments are not checked. Verify the adopted edition with the authority having jurisdiction and a qualified code professional.

Privacy: calculations run locally in your browser; values are not submitted by this tool.

Capacity Factors and Minimum Widths

Code / occupancy	Stairways	Doors, corridors, ramps
IBC 1005.3, standard	0.3 in/person	0.2 in/person
IBC, sprinklered + EVACS (not H, I-2)	0.2 in/person	0.15 in/person
NFPA 101, most occupancies	0.3 in/person	0.2 in/person
NFPA 101, board and care	0.4 in/person	0.2 in/person
NFPA 101, health care nonsprinklered	0.6 in/person	0.5 in/person
NFPA 101, high-hazard contents	0.7 in/person	0.4 in/person

IBC minimum widths: stairway 44 in, or 36 in serving fewer than 50 occupants (1011.2); door 32 in clear (1010.1.1); corridor 44 in general, 36 in under 50 occupants or in a dwelling unit, 72 in Group E with 100 or more, 96 in I-2 bed movement (Table 1020.3); ramp 36 in between handrails (1012.5.1). NFPA 101 uses 44 in (36 in under 50) for new stairs, 32 in for doors and 44 in for new ramps; corridor widths come from the occupancy chapter.

Sources: 2024 IBC Chapter 10 (ICC); NFPA 101 Life Safety Code, Table 7.3.3.1.

How Many People Can a Door or Stair Serve?

Occupant capacity = clear width ÷ factor, rounded down. Minimum widths still apply.

Clear width	Stair 0.3	Stair 0.2	Door/corridor 0.2	Door/corridor 0.15
32 in (813 mm)	106	160	160	213
34 in (864 mm)	113	170	170	226
36 in (914 mm)	120	180	180	240
44 in (1,118 mm)	146	220	220	293
48 in (1,219 mm)	160	240	240	320
56 in (1,422 mm)	186	280	280	373
64 in (1,626 mm)	213	320	320	426
72 in (1,829 mm)	240	360	360	480
88 in (2,235 mm)	293	440	440	586
96 in (2,438 mm)	320	480	480	640

Quick answer

Examples

Occupant load	Door or corridor (0.2 in)	Stairway (0.3 in)
100	20 in → 32 in door min	30 in → 44 in stair min
250	50 in	75 in
450	90 in	135 in
500	100 in	150 in

Enter your occupant load and component to get the governing width, the width per exit and the capacity of existing openings.

Summary

Get the required egress width from the occupant load (the larger of capacity width and the code minimum), split it across exits, or check how many people existing doors and stairs can serve.

How it works

Enter the occupant load served by the component being checked. For a stairway, use the largest single story it serves, not the sum of all stories (IBC 1005.3.1).
Choose IBC 2024 or NFPA 101, the component and, for NFPA, the occupancy that sets the capacity factor.
Capacity width = occupant load × factor. The required width is the larger of that and the dimensional minimum for the component.
Enter the number of exits to see the width each needs if the load is shared equally.
Optionally list existing clear widths (for example "36, 44") to get their combined capacity, check each against the minimum and test the 50% loss-of-one-exit rule (IBC 1005.5).

Use cases

Size stairways, doors and corridors from an occupant load during early design.
Check how many occupants an existing door or stair can serve.
Compare the IBC sprinklered reduction with the standard factor.
Check whether losing the largest exit still leaves half the required capacity.
Compare IBC and NFPA 101 capacity factors for health care and high-hazard occupancies.

Frequently Asked Questions

Last updated: 2026-10-09 · Reviewed by Nham Vu