Occupant load and egress, worked the way plan check will
Occupant Load + Egress Calculator
Two calculators the code makes you run early and often. The first finds the IBC occupant load from a floor area and its function of space, then the number of exits and the egress width that follow. The second checks an emergency escape (egress) window against the IRC (clear area, height, width and sill height) and tells you exactly how far short an opening falls. Every result cites the rule behind it so you can defend it in plan review.
Verify with your jurisdiction This tool applies the 2021 IBC (occupant load, exits and egress width) and 2021 IRC R310 (egress windows). Adopted codes, editions and local amendments vary, and it does not evaluate travel distance, common path of egress, accessibility, occupancy-specific exceptions or the many special provisions. Treat every number as a preliminary check and confirm with the authority having jurisdiction and a licensed design professional.
Occupant load
20
3,000 sq ft ÷ 150 gross · Business · 1 exit required
Emergency escape opening
Compliant
clear opening 7.5 sq ft · IRC R310
How Occupant Load Drives Everything
The occupant load is the first number in the egress chain, and every requirement downstream hangs off it. Get it wrong and the exits, door widths, corridor widths, plumbing counts and even the sprinkler trigger can all be wrong.
The load. Divide the floor area by the occupant load factor from IBC Table 1004.5 and round up. Gross factors (business 150, mercantile 60, storage 300) apply to the whole tenant area; net factors (assembly 7–15, classroom 20, kitchen 200) apply only to the occupied portion of that function.
The exits. One exit is permitted only up to an occupant load of 49, and even then only where travel distance and common-path limits allow. Fifty to 500 occupants need two; 501 to 1,000 need three; above 1,000, four. No single exit may be credited with more than half the required capacity.
The width. Multiply the load by 0.3 inch per occupant for stairways and 0.2 inch for doors and level components, or 0.2 and 0.15 inch in a fully sprinklered, alarmed building. Corridors are 44 inches minimum (36 inches below 50 occupants) and each exit door gives at least 32 inches clear.
Occupant Load Factors (IBC Table 1004.5)
Common functions of space and their occupant load factors. Net applies to the occupied area only; gross applies to the whole floor area.
Function of space
Factor (sq ft/occ.)
Basis
Values follow the 2021 IBC; older editions used 100 gross for business. Confirm the factor and basis for your specific use and edition.
Egress Window Requirements (IRC R310)
Every sleeping room and every basement with habitable space needs an emergency escape and rescue opening that meets all four minimums at once.
Requirement
Minimum
Note
Net clear opening area
5.7 sq ft
5.0 sq ft at grade-floor / below-grade openings
Clear opening height
24 in
Actual free height when open
Clear opening width
20 in
Actual free width when open
Sill height above floor
44 in max
Finished floor to bottom of clear opening
Window well (below grade)
9 sq ft
36 in min horizontal projection & width
The height and width minimums do not by themselves satisfy the area: 24 × 20 in is only 3.3 sq ft. One dimension has to grow to reach 5.7 sq ft. Wells deeper than 44 in need a permanently affixed ladder or steps.
Frequently Asked Questions
How do you calculate occupant load?
Floor area ÷ occupant load factor, rounded up. A 3,000 sq ft office at 150 gross is 20 occupants; a 2,000 sq ft restaurant dining room at 15 net is 134.
How many exits does a space need?
One up to 49 occupants (with travel-distance limits), two from 50–500, three from 501–1,000, four above 1,000. Assembly and hazardous uses are stricter.
What size does an egress window have to be?
At least 5.7 sq ft clear opening (5.0 at grade), 24 in minimum height, 20 in minimum width, sill no more than 44 in above the floor.
Is a 24 × 20 inch window big enough?
No. That meets the minimum height and width but is only 3.3 sq ft, well below 5.7. You need a larger opening; the checker shows the width or height required to get there.
How wide do exit doors and corridors need to be?
Doors give at least 32 in clear; total egress width is the occupant load × 0.2 in (doors) or 0.3 in (stairs), less with sprinklers. Corridors are 44 in, or 36 in under 50 occupants.
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