How do you calculate occupant load?

Divide the floor area of each space by the occupant load factor for its function in IBC Table 1004.5, and round up — a fraction of an occupant counts as a whole occupant. Business areas are 150 sq ft gross per occupant, mercantile 60 gross, assembly with tables and chairs 15 net, assembly with chairs only 7 net. Mixed-function floors are calculated space by space and then summed.

What is the difference between gross and net floor area?

Gross area is measured to the inside face of the exterior walls and includes circulation, mechanical and accessory space. Net area excludes those. Table 1004.5 states which basis each function uses, and using the wrong one changes the answer substantially.

How much egress width does an occupant load require?

IBC 1005.3.1 requires 0.3 inch of stairway width per occupant and 1005.3.2 requires 0.2 inch for doors, corridors and other components. In a building sprinklered under 903.3.1.1 or 903.3.1.2 AND fitted with an emergency voice/alarm system under 907.5.2.2, those drop to 0.2 and 0.15. Group H and Group I-2 occupancies cannot use the reduced factors.

When is one exit allowed?

IBC Table 1006.2.1 sets the ceiling by occupancy: 49 occupants for Groups A, B, E, F, M and U; 29 for Group S; 20 for R-2, R-3 and R-4; 10 for most institutional and R-1; and 3 for H-1 through H-3. Above that, two exits are required, three above 500 occupants, and four above 1,000.

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Occupant Load & Egress Width Calculator

Occupant load per IBC Table 1004.5, then the egress width and exit count that load requires under IBC 1005.3 and Table 1006.2.1. Add a row per space — a mixed-function floor is calculated space by space, each rounded up on its own, then summed.

Spaces

Occupancy Group

Sets the single-exit threshold in Table 1006.2.1

Sprinklers + voice alarmNo

903.3.1.1/903.3.1.2 and907.5.2.2 — sprinklers alone don’t qualify

Results

Business areas4,500 sq ft gross ÷ 150 = 30.00, rounded up	30
Assembly without fixed seats — Unconcentrated (tables and chairs)900 sq ft net ÷ 15 = 60.00, rounded up	60
Total occupant load	90

Stairway width

27 in

90 × 0.3 in — IBC 1005.3.1

Doors & corridors

18 in

90 × 0.2 in — IBC 1005.3.2

Exits required

One exit allowed to 49 occupants

Reference only. This covers the base calculation. It does not apply fixed-seating provisions (1004.6), concentrated business use (1004.8), multiple-story convergence, smoke-protected assembly seating, minimum component widths, or the effect of losing one exit. Verify with the adopted code edition and your building department.