Calculating the occupant load

Occupant load means the number of people allowed in a building, space, or room.

It’s determined by:

• how areas are used
• the building’s occupancy classification
• the building’s egress system, including
  • number of exits
  • total width of all exits, ramps, and stairwells

There are 2 calculations to do and compare:

1. Floor area occupant load
2. Exit width occupant load

The calculation with the lower number is the occupant load for the building, space, or room.

Ottawa Fire Services is not able to calculate the occupant load for you. Contact a qualified architect or engineer if you cannot do the calculation yourself.

A gymnasium is set up for a lunch event with tables and chairs. There are four exits with double-doors from the gymnasium and each double-door is 2200 mm wide. To get to each exit door, there is a short stairwell.

Floor area occupant load

Step 1 - Calculate the area of the room/building/space

Length x Width = Area

Example: The gymnasium is 30.5 metres x 18.0 metres. The total area is 540 m²

Step 2 – Determine occupant load factor

To determine the occupant load factor, refer to the appropriate table in the Occupant load area per person (table 3.1.17.1).

Example: The lunch event in the gymnasium would be classified as a space with non-fixed seats and tables. From Table 1: Assembly uses, we can determine the occupant load factor is 0.95 m² of space per person.

Step 3 – Apply occupant load factor and round down to whole number

Total area / occupant load factor = number of persons

Example: 540 m²/0.95 m² per person = 577.9

Rounding down, 577 people

Exit width occupant load

In this example, the gymnasium has four exits with double doors and each double-door is 2200 mm wide. There is a small stairwell for each exit.

Step 1: Calculate the width of the exits

Number of exits x width of exit = total width of exits

If there is more than one exit, no single set of doors can account for more than half the occupants

Total width of exits x 50% = calculated exit width

Example: The gymnasium has four exits with double doors and each double-door is 2200 mm wide. There is a small stairwell for each exit.

4 exits x 2200 mm = 8800 mm

Remember: when more than one exit is available from a floor area, no single set of doors can account for more than half the occupants.

8800mm x 50% = 4400mm

The calculated exit width is 4400 mm.

Step 2: Determine the exit width occupant load factor

To determine the exit width factor, refer to subsection 3.4.3.2. Exit width.

In this example, there is a small stairwell for each exit, so the exit width factor would be 8 mm as per Section 1(b): 8 mm per person for a stair consisting of steps whose rise is not more than 180 mm and whose run is not less than 280 mm.

Step 3: Apply exit width occupant load factor and round down to whole number

Calculated exit width / occupant load factor = number of persons

4400mm ÷ 8mm = 550 people

Compare calculations

The allowed number of occupants is the lowest of the two calculations. From the example above:

Floor area calculation is 577 people

Exit width calculation is 550 people

So, the occupant load for the lunch event at the gymnasium is 550 people.

These tables are available for reference purposes only. For up-to-date information, view the Ontario Building Code and navigate to Subsection 3.1.17 Occupant Load.

This information is available for reference purposes only. For up-to-date information, view the Ontario Building Code and navigate to Article 3.1.17 Occupant Load.

Excerpt from 3.1.17.1 Occupant load determination

1. The occupant load of a floor area or part of a floor area, or of a building or part of a building not having a floor area, shall be based on,
   1. the number of seats in an assembly occupancy having fixed seats,
   2. two persons per sleeping room or sleeping area in a dwelling unit or suite, or
   3. the number of persons,
      1. for which the area is designed, or
      2. determined from the table below for occupancies other than those described in (a) and (b) from above.
2. If a floor area or part of it has been designed for an occupant load other than that determined from Table 3.1.17.1., a permanent sign indicating that occupant load shall be posted in a conspicuous location.
3. For the purposes of this Article, mezzanines, tiers, and balconies shall be regarded as part of the floor area.
4. If a room or group of rooms is intended for different occupancies at different times, the value to be used from Table 3.1.17.1. shall be the value that gives the greatest number of persons for the occupancies concerned.
5. Except as provided by Sentence (6) or (7), in dining, alcoholic beverage and cafeteria spaces the occupant load shall be determined from Table 3.1.17.1.
6. The occupant load in Sentence (5) is permitted to be the number of persons for which the space is designed.
7. The occupant load in Sentence (6) shall be not more than that determined by using an area of 0.6 m2 per person.

3.1.17.2 Dance floor

The occupant load of a room in which a dance floor is situated shall be calculated in respect of that portion of the room that is not occupied by the dance floor.

This information is available for reference purposes only. For up-to-date information, view the Ontario Building Code and navigate to Article 3.4.3.2. Exit width.

Excerpt from 3.4.3.2. Exit width

1. Except as permitted by Sentence (3), the minimum aggregate required width of exits serving floor areas intended for assembly occupancies, residential occupancies, business and personal services occupancies, mercantile occupancies, and industrial occupancies shall be determined by multiplying the occupant load of the area served by,
   1. 6.1 mm per person for ramps with a slope of not more than 1 in 8, doorways, corridors, and passageways,
   2. 8 mm per person for a stair consisting of steps whose rise is not more than 180 mm and whose run is not less than 280 mm, or
   3. 9.2 mm per person for,
      1. ramps with a slope of more than 1 in 8, or
      2. stairs, other than stairs conforming to Clause (b).
2. The minimum aggregate width of exits serving floor areas intended for a care, care and treatment or detention occupancy shall be determined by multiplying the occupant load of the area served by 18.4 mm per person.
3. The minimum aggregate width of means of egress serving a Group A, Division 4 occupancy shall be determined by multiplying the occupant load of the area served by,
   1. 1.8 mm per person for,
      1. aisles,
      2. stairs other than exit stairs, and
      3. ramps and passageways in vomitories and exits, and
   2. 2.4 mm per person for exit stairs.
4. Except as required by Sentence (5), the required exit width need not be cumulative in an exit serving two or more floor areas located one above the other.
5. The required exit width for an exit stair in an assembly hall or theatre serving more than one balcony level shall conform to the appropriate requirements for stairs serving interconnected floor spaces in Article 3.2.8.4.
6. If more than one exit is required, every exit shall be considered as contributing not more than one-half of the required exit width.
7. The width of an exit shall be not less than,
   1. 1 100 mm for corridors and passageways,
   2. 1 100 mm for ramps not serving patients’ or residents’ sleeping rooms,
   3. 1 100 mm for stairs, not serving patients’ or residents’ sleeping rooms, that serve more than two storeys above the lowest exit level or more than one storey below the lowest exit level,
   4. 900 mm for stairs, not serving patients’ or residents’ sleeping rooms, that serve not more than two storeys above the lowest exit level or not more than one storey below the lowest exit level,
   5. 1 650 mm for stairs and ramps serving patients’ or residents’ sleeping rooms,
   6. 1 050 mm for doorways serving patients’ or residents’ sleeping rooms, and
   7. 790 mm for doorways not serving patients’ or residents’ sleeping rooms.