Occupancy Calculator
Enter the floor area and pick how the space is used. The calculator divides the area by the occupant load factor from the International Building Code and shows how many people the space is designed for.
Table 1004.5 occupant load factors (IBC 2021)
Maximum floor area allowances per occupant from the International Building Code 2021, Table 1004.5, as used by this calculator. Rows that the table sends to another section (assembly with fixed seats, concentrated business use areas, mall buildings) are not included.
How to use the occupancy calculator
Choose square feet or square meters, then type the floor area, or switch to Length x width and type the size of the room. Pick the use of the space from the list, for example Unconcentrated (tables and chairs) for a banquet room or Classroom area for a school room. The big number is the occupant load: the area divided by the factor, rounded up to a whole person.
A building with several uses gets one line per area: press + Add another area for the dining room, the bar, the kitchen and so on, and the calculator adds them up. Each line shows its own sum, so you can check the working. Custom factor takes any factor you are given, for example by your local code. Print sheet prints the calculation with the source, and Share link copies the areas and uses, so a colleague opens the same calculation.
Once the doors are open, the attendance counter counts people in and out and warns you as the number inside nears the capacity you enter.
Occupant load factors from IBC 2021 Table 1004.5
The factors come from Table 1004.5, Maximum Floor Area Allowances per Occupant, in the 2021 edition of the International Building Code (IBC). Each factor is a floor area in square feet per occupant, measured either gross or net as the table says. Gross floor area is measured inside the exterior walls without deducting corridors, stairways, closets, interior walls or columns. Net floor area is the occupied area only, leaving out accessory areas such as corridors, stairways, toilet rooms, mechanical rooms and closets.
Worked example for a 1,200 sq ft room: with tables and chairs (15 sq ft net per person) it is 1,200 / 15 = 80 people; with chairs only (7 sq ft net) it is 1,200 / 7 = 171.4, shown as 172; as standing space (5 sq ft net) it is 240. That is why a seating capacity calculator gives such different answers for the same room. The full list of factors is under Table 1004.5 occupant load factors below the calculator. Seats that are fixed to the floor are counted by the seats rather than by area (Section 1004.6), so they are not in this calculator.
This is an estimate for planning, not an approval. Cities and states adopt different editions of the code, sometimes with their own changes, and the building official or fire marshal decides the approved occupant load, which can also be limited by exits, doors and other rules the table does not cover. Check with them before you post a maximum occupancy sign.
Keyboard shortcuts
- A: add another area
- U or Ctrl+Z: undo
- Tab: move between the fields
- F: full screen
Questions
How do I calculate the capacity of a room?
Divide the floor area by the occupant load factor for how the room is used. In square feet, a 600 sq ft classroom at 20 sq ft net per person holds 600 / 20 = 30 people. The room capacity calculator above does this for you and adds up several areas.
Can I use square meters?
Yes. Press Square meters. The factors in the code are in square feet, so the calculator converts them (1 sq ft is 0.09290304 sq m) and shows them in square meters too. Switching units converts the sizes you typed, so the result stays the same.
Why is my answer different from the number on the sign?
The posted number is set by the local authority. It can be lower than the area calculation because of the number and width of exits, the fixed seating, or local amendments to the code, and a different code edition can use different factors.
Which edition of the building code does it use?
The 2021 International Building Code, Table 1004.5. Your jurisdiction may have adopted an older or newer edition; if its factor differs, choose Custom factor and type it in.
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Put this occupancy calculator on your website
Free for classrooms, clubs, blogs and shops: paste this code into any page. It works the same inside your site, and counts stay in each visitor's own browser. For a dark version, add ?theme=dark after /occupancy-calculator/ in the code.