How do I calculate occupant load?

Floor area divided by the load factor for that function of space from IBC Table 1004.5, rounded up. The trap is that some factors are against gross floor area and some against net, and the two are not interchangeable.

What is the occupant load factor for an office?

Business areas are 150 sq ft gross per occupant. A 3,000 sq ft office suite is therefore 20 occupants.

What is the difference between gross and net floor area?

Gross is everything inside the exterior walls including corridors, toilet rooms and closets. Net is the usable area of the function itself with those excluded. Table 1004.5 specifies which applies for every row and they are not close.

What is the occupant load factor for a restaurant?

Assembly without fixed seats, unconcentrated with tables and chairs, is 15 sq ft net. Standing space is 5 sq ft net and concentrated chairs-only seating is 7 sq ft net.

At what occupant load do I need two exits?

Generally above 49, and above 500 a third is required. But travel distance and common path of egress travel limits can force a second exit at any occupant load, so the count alone does not settle it.

Does occupant load apply to a house?

No. It is an IBC calculation and does not apply to a detached single-family dwelling under the IRC. There is no occupant load number for a house.

Does fixed seating change the calculation?

Yes. Where fixed seats are installed the occupant load is the number of seats, not an area calculation. Booths and bench seating are measured by length under a separate provision.

Home › Structural › Occupant Load Calculator

Occupant Load Calculator

IBC Table 1004.5, every row, with gross and net marked

Occupant load is one division, and almost everyone gets it wrong in the same place: the table gives some factors as gross floor area and some as net, and the two are not close. Business areas are 150 sq ft gross. An assembly space with chairs is 7 sq ft net. This carries every row of IBC Table 1004.5 with the gross or net marked.

Occupant load and egress width

Floor area (gross or net, as the row requires)

sq ft

Function of space

Fixed seats (0 if none, overrides the calculation)

no.

Exits provided

no.

Sprinklered with alarm

Factors are IBC Table 1004.5 as adopted in Washington State. Egress widths use the IBC 1005.3 factors.

Specification summary

Generated from on . Reopen that address to reproduce these figures exactly.

Entered

Result

Occupants, and the exit width they require

Worked example

A 3,000 sq ft office suite, sprinklered, with two exits.

Factor. Business areas is 150 sq ft gross per occupant.
Load. 3,000 / 150 = 20 occupants.
Egress. 20 × 0.15 in = 3.0 in, which is nothing: the minimum door and corridor widths govern entirely.
Now change it to a restaurant with tables and chairs at 15 sq ft net: 200 occupants, ten times as many.
Egress becomes 30 in, and above 49 occupants you are into two exits as a matter of course.

The office to restaurant change is the whole point of the table. Same floor, ten times the people, and a completely different building from an egress and occupancy standpoint.

The formula

One division and one multiplication, with the units doing all the damage:

occupants = ⌈ area / factor ⌉ width = occupants × 0.15 (0.2 unsprinklered)

area: GROSS or NET as the row specifies. They are not interchangeable
factor: sq ft per occupant from Table 1004.5
0.15 / 0.2: in per occupant for doors and corridors, sprinklered and not
0.2 / 0.3: in per occupant for stairways, sprinklered and not

Egress width is almost never the governing number in a small building: minimum door and corridor widths are wider than the calculation demands until the occupant load gets into the hundreds. It matters in assembly spaces and stairs.

Gross and net are the whole difficulty

The arithmetic is trivial. The difficulty is that Table 1004.5 gives some factors against gross floor area and some against net, and the difference is large.

Gross is everything inside the exterior walls: corridors, toilet rooms, closets, mechanical space. Net is the usable area of the function itself with those excluded. A 3,000 sq ft floor might be 3,000 gross and 2,200 net, and where the factor is small that difference moves the occupant load by dozens of people.

The pattern is that assembly and educational functions, where people are packed in, tend to be net, and business, storage and industrial tend to be gross. But it is not a rule you can rely on: exhibit gallery is net at 30, gaming floors are gross at 11. Read the row.

The other thing worth knowing is that occupant load is not a limit on how many people may be in a room. It is the number the building's exits, corridors and plumbing fixtures are designed for. A space with a posted capacity has had that number derived from this table and then possibly reduced by something else.

This is an IBC calculation, not an IRC one

Occupant load lives in the International Building Code, Chapter 10, and applies to commercial, assembly, institutional, mercantile and multi-family buildings. It does not apply to a detached single-family dwelling, which is governed by the IRC and has no occupant load calculation at all.

Most of the rest of this site is IRC. This page is the exception, and it is here because the question is asked constantly by people fitting out shops, offices and restaurants.

If you are working on a house and looking for how many people it holds, there is no such number in the residential code. What the IRC does constrain is egress from the dwelling: one exit door, and an emergency escape opening from sleeping rooms.

What occupant load actually drives

Number of exits. Broadly, more than 49 occupants needs two and more than 500 needs three, but travel distance and common path of egress travel can force a second exit at any load, and those are not functions of occupant count.

Egress width. IBC 1005.3 sets 0.2 in per occupant for stairways and 0.15 for other components in a sprinklered building with an alarm, and 0.3 and 0.2 without. Minimum component widths apply regardless and usually govern in small buildings.

Plumbing fixture counts, which come from the occupant load through a separate table entirely and are frequently the thing that actually constrains a restaurant fit-out.

Whether the space is an assembly occupancy, which changes the construction, alarm and sprinkler requirements considerably. Fifty occupants is a threshold that turns an ordinary room into an A-occupancy.

Frequently asked questions

How do I calculate occupant load?: Floor area divided by the load factor for that function of space from IBC Table 1004.5, rounded up. The trap is that some factors are against gross floor area and some against net, and the two are not interchangeable.
What is the occupant load factor for an office?: Business areas are 150 sq ft gross per occupant. A 3,000 sq ft office suite is therefore 20 occupants.
What is the difference between gross and net floor area?: Gross is everything inside the exterior walls including corridors, toilet rooms and closets. Net is the usable area of the function itself with those excluded. Table 1004.5 specifies which applies for every row and they are not close.
What is the occupant load factor for a restaurant?: Assembly without fixed seats, unconcentrated with tables and chairs, is 15 sq ft net. Standing space is 5 sq ft net and concentrated chairs-only seating is 7 sq ft net.
At what occupant load do I need two exits?: Generally above 49, and above 500 a third is required. But travel distance and common path of egress travel limits can force a second exit at any occupant load, so the count alone does not settle it.
How much egress width does an occupant load require?: IBC 1005.3 gives 0.2 in per occupant for stairways and 0.15 for other components in a sprinklered building with an alarm, and 0.3 and 0.2 without. Minimum door and corridor widths apply regardless and usually govern in small buildings.
Does occupant load apply to a house?: No. It is an IBC calculation and does not apply to a detached single-family dwelling under the IRC. There is no occupant load number for a house.
Does fixed seating change the calculation?: Yes. Where fixed seats are installed the occupant load is the number of seats, not an area calculation. Booths and bench seating are measured by length under a separate provision.

Check these numbers yourself

IBC Table 1004.5 as adopted in Washington State, WAC 51-54A-1004Washington State Legislature, effective 15 March 2024. The full table with gross and net marked for every row. Used because codes.iccsafe.org returns HTTP 403.
IBC Chapter 10, means of egressUpCodes. Section 1005.3 egress width factors and the exit count provisions. Confirm the edition and jurisdiction it serves you.

How every figure here is verified: Sources & Method. Who builds this: About. Found something wrong? Tell us and it gets fixed or removed.

Figures on this page last checked against the source documents on 2026-09-08. Codes are amended locally; confirm against the edition your jurisdiction enforces.

Related calculators

This is an IBC calculation and does not apply to a house. Factors are the table as adopted in Washington State; other jurisdictions amend it. Whether a row uses gross or net floor area changes the answer substantially, so read the row. Exit counts also depend on travel distance and common path limits, which are not a function of occupant load.