Occupant Load Calculator

About This Tool

Both model codes size means of egress from the occupant load, the number of people a space is designed for. For spaces without fixed seats it is the floor area divided by an occupant load factor, in square feet (or square meters) per person, set by the use of the space: about 150 ft² gross for offices, 15 ft² net for tables and chairs, 7 ft² net for chairs only, and up to 500 ft² gross for warehouses. Gross area is measured inside the exterior walls and includes corridors, stairs, toilets and mechanical rooms; net area is only the occupied part of the room. Fixed seating counts the seats. The calculator rounds each area up to a whole person and adds the areas on the story.

The egress width needed is the occupant load times a capacity factor: 0.3 in. per person for stairs and 0.2 in. per person for doors, corridors, ramps and other level components in most occupancies. The IBC lowers these to 0.2 and 0.15 in. in buildings sprinklered throughout with an emergency voice/alarm communication system (other than Group H and I-2). NFPA 101 uses higher factors for board and care, nonsprinklered health care and high hazard contents. The number of exits per story is at least two, three for more than 500 occupants and four for more than 1,000. The required width is then split among the exits, with no single exit carrying more than half of it, and each stair and door must still meet its minimum size.

Worked example

An office floor has 14,000 ft² of open office at 150 ft² gross (94 people), 1,500 ft² of conference rooms and a 600 ft² break room at 15 ft² net (100 and 40 people), and 900 ft² of storage and mechanical space at 300 ft² gross (3 people). The occupant load is 237. Under the IBC standard factors the stairs need 237 × 0.3 = 71.1 in. in total and the doors and corridors 237 × 0.2 = 47.4 in. Two exits are required; split between two stairs that is 35.6 in. each, so the 44 in. minimum stair width governs, and each exit door needs at least 32 in. of clear width.

Assumptions and limits

The tables in the calculator are the common rows of the current IBC and NFPA 101 tables, not every row and footnote; use the “other” option for uses not listed and confirm the factor with the adopted code. Local amendments, mixed occupancy rules, mezzanines, egress from floors above and below converging on a floor, travel distance, common path and dead ends are not checked. The NFPA 101 occupancy chapters can change the factors and the number of exits, and an authority having jurisdiction may set a higher posted occupant load.

When to bring in an engineer

Occupant load drives the rest of the life safety plan: exit count, stair and door sizes, plumbing fixtures, sprinkler and alarm triggers. DGA prepares life safety and egress plans and code consulting for change of use, assembly spaces and performance-based egress designs.

References

1. International Code Council, International Building Code, 2024 edition: Section 1004 (occupant load, Table 1004.5), Section 1005 (egress width, 1005.3.1 and 1005.3.2), Section 1006 (number of exits, Table 1006.3.3), Section 1010.1.1 and Section 1011.2 (minimum widths).
2. NFPA 101, Life Safety Code, National Fire Protection Association, 2024 edition: 7.3.1 (occupant load, Table 7.3.1.2), 7.3.3 (egress capacity, Table 7.3.3.1) and 7.4.1 (number of means of egress).
3. National Bureau of Standards, Design and Construction of Building Exits, Miscellaneous Publication M151, U.S. Department of Commerce, 1935: the field studies behind exit width units and capacity.