How to use the occupancy load calculator
Occupant load is the number of people a building code assumes can be in a space at once. It sets how many exits you need, how wide doors, corridors and stairs must be, and how many plumbing fixtures to provide. Getting it early stops a floor plan from being drawn around an exit strategy that does not work.
- Choose the area unit and whether the building has sprinklers with an emergency voice/alarm system, which changes the egress width factors.
- For each space, pick its function from the IBC Table 1004.5 list and enter its area. Use gross or net area as the factor states.
- Add up to three spaces, such as a restaurant's dining room, bar and kitchen. Leave unused spaces at zero.
The results show the occupant load for each space, the total, the usual number of exits for a story with that load, and the minimum egress width for stairs and for other components.
Occupant load formulas
Occupant load = Area ÷ Load factor (round up)
Total = Sum of the spaces
Stair width = Occupants × 0.3 in (0.2 in with sprinklers + voice alarm)
Other egress width = Occupants × 0.2 in (0.15 in with sprinklers + voice alarm)
| Function of space (IBC Table 1004.5) | ft² per occupant |
|---|---|
| Assembly, concentrated (chairs only, not fixed) | 7 net |
| Assembly, standing space | 5 net |
| Assembly, unconcentrated (tables and chairs) | 15 net |
| Business areas | 150 gross |
| Concentrated business use areas | 50 gross |
| Educational, classroom area | 20 net |
| Exercise rooms | 50 gross |
| Kitchens, commercial | 200 gross |
| Library reading rooms / stack area | 50 net / 100 gross |
| Mercantile | 60 gross |
| Residential | 200 gross |
| Industrial areas | 100 gross |
| Accessory storage, mechanical equipment room | 300 gross |
These are the 2021 IBC values. Check the edition and any local amendments adopted where you are building.
Worked examples
A 3,000 ft² office floor
Business areas use 150 ft² gross per person: 3,000 ÷ 150 = 20 occupants. That is well under 500, so a story with this load needs two exits, and a single room of this size may qualify for one exit if travel distances work. Egress width for other components is 20 × 0.2 = 4 inches, so the code minimum door and corridor widths govern instead.
A restaurant
A 1,800 ft² net dining room at 15 ft² per person holds 120 people. A 300 ft² standing bar area at 5 ft² adds 60. A 600 ft² gross kitchen at 200 ft² adds 3. The total is 183 occupants, which needs two exits; without sprinklers, stair width would be 183 × 0.3 = 54.9 inches.
A metric classroom
A 70 m² classroom is about 753 ft². At 20 ft² net per person, the occupant load is ⌈753 ÷ 20⌉ = 38 students. Being under 50, a single exit door may be acceptable for the room, subject to travel distance rules.
Who this calculator helps
- Architects testing exit strategy, door counts and stair widths at concept stage, before life safety plans are drawn.
- Interior designers planning restaurant, office and retail fit-outs where a layout change can alter the occupant load.
- Code consultants and fire engineers running quick checks against a full code analysis.
- Facility and event managers understanding the posted capacity of a room.
- Architecture students learning how occupancy drives plan layout and egress.
Tips for occupant load and egress
- Calculate each functional area separately; one factor for a whole mixed-use floor usually over- or underestimates.
- Measure the areas with the square footage calculator, and size egress stairs with the stair calculator.
- If a level change sits on an accessible route, check it with the ADA ramp slope calculator.
- Occupant load also drives plumbing fixture counts, so share the number with the services engineer early.
- Keep a code summary sheet in the drawings with the factors, areas and totals you used.
Planning a fit-out? Show the client how the space could look with furniture in place using Virtual Staging.
