IBC Section 1004.5 — Occupant Load:
"The occupant load of a room or space shall be determined by dividing the floor area assigned to that use by the occupant load factor for that use as specified in Table 1004.5."

IBC Section 1004.1 — Design Occupant Load:
"The number of occupants shall be computed at the rate of one occupant per unit of area as prescribed in Table 1004.5. For areas without a specified occupant load in Table 1004.5, the building official shall establish the occupant load."

Selected factors from IBC Table 1004.5:

Function of Space	OL Factor (gross sq ft/person)
Assembly — standing space	5
Assembly — concentrated (chairs only, not fixed)	7
Assembly — less concentrated (tables & chairs)	15
Assembly — unconcentrated (standing/movable seating)	15
Assembly — gaming floors	11
Assembly — stadium/arena seating	See fixed seating note
Business / office areas	150
Mercantile — basement / ground floor	30
Mercantile — upper floors	60
Restaurant / lounge area	15
Kitchen / commercial	200
Storage areas / mechanical equipment rooms	300
Lobby / foyer / pre-function	100
Corridors / passageways	See egress width calc

Fixed or Bleacher Seating: Where fixed seating is used, the occupant load is the number of fixed seats installed. For bleachers, one person per 18 linear inches of seating length.

Mixed Occupancy: In spaces with multiple functions, calculate each area separately using its applicable factor. The sum is the total occupant load for egress and staffing purposes.

Why occupant load drives egress requirements:
The occupant load calculated here directly determines the minimum required egress capacity under IBC Chapter 10 and NFPA 101 Chapter 7. Specifically:

IBC 1005.1 — Minimum Egress Width: Each component of the means of egress shall not be less than the width required by the component's individual minimum width requirement. The total width of egress components is determined by multiplying the occupant load by the applicable egress factor (0.2 inches per occupant for stairways; 0.15 inches per occupant for other egress components).

IBC 1006.3 — Minimum Number of Exits:

Occupant Load	Minimum Exits
1–500	2
501–1,000	3
More than 1,000	4

Note: These are minimums. AHJ review, occupancy type, high-rise provisions, and specific use conditions may require additional exits or width. Always confirm with your local building official.

Gross vs. Net Area: Most IBC Table 1004.5 factors use gross floor area — the total floor area within the enclosing walls, including columns, interior walls, and structural elements. Some uses specify net floor area (area actually occupied, excluding walls, columns, etc.). This calculator uses gross area for all zones, consistent with the majority of assembly occupancy factors.

Outdoor Areas: For outdoor assembly areas (plazas, lawns, amphitheaters), calculate based on the assigned or fenced assembly area, not total site area. Use the same IBC factors; the same egress requirements apply.

Zones Must Not Overlap: Each square foot of floor area should be counted in only one zone. Mechanical rooms, restrooms, and service corridors are typically excluded from occupant load calculations but may be required for egress planning.

AHJ Discretion: IBC Section 1004.1 grants the building official authority to establish occupant loads for uses not listed in Table 1004.5, and to approve alternate calculation methods where justified. This tool applies the standard code factors — local authority may modify them.

Fixed Seating Override: Where an assembly area has fixed or permanently installed seating (theater seats, bleachers), the occupant load is the actual seat count — not calculated from floor area. Use the actual count for those zones.