Occupancy Load Calculator NZ: How It Works

An occupancy load calculator for New Zealand works out the maximum number of people a room or building can safely hold, based on its floor area and the activity happening inside. You enter the room’s usable floor area in square metres and select the type of space (e.g., office, classroom, retail), and the calculator returns the maximum occupant number using the load factors from NZ Building Code clauses. This article explains the formula, where the numbers come from, and how to apply them correctly to a real building.

Formula

The core formula is simple:

Maximum occupants = Floor area (m²) ÷ Load factor (m² per person)

Where:

• Floor area (A) – the usable floor area of the room or space, measured in square metres. This excludes walls, columns, and fixed obstructions.
• Load factor (L) – the amount of floor area required per person, in square metres per person. This varies by the type of occupancy and is defined in the NZ Building Code (Clause C1 and Acceptable Solution C/AS1).

Worked Example

Using the calculator’s default values: a 100 m² office with a load factor of 1.0 m²/person.

1. Identify floor area: A = 100 m²
2. Identify load factor for an office: L = 1.0 m²/person
3. Apply the formula: 100 ÷ 1.0 = 100 people

The calculator shows 100 maximum occupants. If the same space were a classroom (L = 1.5), it would be 100 ÷ 1.5 = 66.7, rounded down to 66 people.

Where the Load Factors Come From

New Zealand’s Building Code sets out minimum load factors for different space uses. These are not arbitrary – they are based on the space needed for a person to move, sit, or stand safely, and they account for evacuation scenarios. The Acceptable Solution C/AS1 provides a table of “area per person� values for common building types:

• Offices – 1.0 m²/person
• Classrooms – 1.5 m²/person
• Retail shops – 2.0 m²/person
• Assembly areas (without fixed seats) – 0.5 m²/person
• Dining areas – 1.0 m²/person
• Workshops – 3.0 m²/person

These are the values used in the calculator. Note that some spaces, like theatres or stadiums, have different factors based on fixed seating or standing room – those are not covered here.

How to Use the Result Correctly

The calculated number is a maximum – it is the limit for safety, not a target. You should use it for:

• Checking if a room can hold a planned event or class size.
• Determining the number of exits and exit widths required (the occupant load drives egress design).
• Setting a capacity sign for public spaces.

Remember that the result is based on the usable floor area – subtract areas taken up by counters, stages, or large furniture. If the room has multiple uses, use the most restrictive (lowest) load factor.

Common Mistakes and Misconceptions

One frequent error is using the gross floor area (including walls) instead of the net usable area. This can overestimate the safe capacity by 10–20%. Another mistake is mixing units – the formula works only with square metres and square metres per person. If you measure in feet, convert first (1 m² = 10.764 ft²).

Also, the load factor is not the same as “square footage per person� used in some other countries (like the US). NZ values are generally more conservative for assembly spaces. Finally, the calculated number is a starting point – a building official may require a lower number based on exit capacity or fire safety features.

Limits of the Formula

The simple area-based formula does not account for:

• Exit capacity – if the exits are narrow or few, the actual safe occupancy may be lower.
• Fixed seating – if the room has fixed seats, the number of seats is the limit, not the area.
• Special hazards – laboratories, kitchens, or areas with flammable materials may have lower limits.
• Accessibility – wheelchair spaces and circulation paths reduce usable area.

For these situations, consult a fire engineer or building official. The calculator gives a quick estimate, but the final occupancy must be determined by a professional using the full Building Code.

Frequently Asked Questions

What is the load factor for a restaurant in NZ?

For dining areas, the Acceptable Solution C/AS1 typically uses 1.0 m² per person. This covers seated dining. If you have a bar or standing area, that may be different – often 0.5 m² per person for standing.

Does the occupancy load include staff?

Yes, the maximum occupants includes everyone in the space – staff, customers, visitors. It is a total count, not just the public.

Can I use this calculator for a house?

It is not necessary for a private dwelling. The Building Code does not set occupancy limits for typical homes – they are designed for family use. This calculator is for public or commercial spaces.

What if my room has an irregular shape?

Calculate the floor area accurately – divide the space into rectangles or use a floor plan. The formula only needs the total usable area, not the shape.

Is the result legally binding?

No. Only a building official (e.g., from your local council) can approve a final occupancy load. This calculator is an educational tool to help you estimate and understand the process.

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in a | Floor area | m² | 100 | 0
sel u | Space type | Office=1, Classroom=1.5, Retail=2, Assembly=0.5, Dining=1, Workshop=3
out n | Maximum occupants | people | a / u | 0
out d | Area per person | m²/person | u | 2