Air Conditioner Size Calculator

What Air Conditioner Size Do You Need?

For an air conditioner to effectively control and treat the heat load of the air in a given space, it is important to calculate the correct air conditioner size of the unit needed for that environment. It is better to have a qualified air conditioner installer do a precise on-site assessment as there are a number of different factors to consider. The following information will however give you an approximate guide to the air conditioner capacity required for a particular area.

Number Of People In The Area & Level Of Activity:

An office with one person and an office of the same size with eight people is different. A person seated at an office desk gives off less heat than someone who is more active like in an office reception area or a restaurant filled with people eating and drinking. Add 400-600 BTU / person (average) depending on activity.

How To Calculate The Heat Load

Here follows a guide only. For offices, homes and your average area requiring air conditioning always keeps the following factors in mind:

Curtains & Blinds:

A room area or office space with blinds or glazed windows for direct sunlight protection, the heat gain is reduced.


The power of an air conditioner is measured in BTU’s (British Thermal Units).

To convert BTU’s into Kw: BTU x 0.0002928 = kW

Open Doors & Windows:

If outside air is added to an area, this air will be warmer than the air in the given area and will need to pass through the refrigeration cycle to lower its temperature thereby causing the air conditioner to work at a greater load, thus the capacity is affected.

For Additional Heat Loads To BTU, The Following Calculation/s Could Be Used:

People – Add 400-600 BTU / person (average) depending on activity

Electrical Equipment � Wattage x 3.4 = BTU (e.g. a 100W light = 100 x 3.4 = 340 BTU)

Electrical Equipment In Use:

The heat load in an empty office in a building with no people in it might not be much compared to the heat generated by the equipment in a computer room. This extra generated heat will increase the heat load, affecting the capacity. An excessive number of lights will have a similar effect. Should the area being calculated be considered a standard heat load, then the following average heat load calculation could be used: 600 BTU / m².

Exposure To Direct Sunlight:

Take into account excessive heat gain from large or multiple windows or a non-insulated roof.

Type Of Building Construction:

A construction of bricks will generally be cooler than timber or metal.

Size Of The Area (m²):

To determine the BTU size of the unit, the size of the area to be treated must be calculated:

Length of room x width = m²

If the height of the ceiling is over 3m, then add on the increased percentage of the area.

Please use the table below to help calculate the size of your room by multiplying the length of your room by the width.

For a room of approximately: Air conditioner size required:
10 to 15 m² 9 000 BTU
16 to 20 m² 12 000 BTU
21 to 30 m² 18 000 BTU
31 to 40 m² 24 000 BTU
41 to 50 m² 30 000 BTU

Air Conditioner Size Power Supply:

The following air conditioning units do not need a separate power supply and can be plugged into a wall socket:

Room size of up to 15m² = 9 000 BTU (2.6Kw)

Room size 18m² – 20m² = 12 000 BTU (3.5Kw)

Room size 24m² – 30m² = 18 000 BTU (5.3Kw)

The Following Air Conditioning Units Need A Separate Power Supply To Be Installed To Which The Unit Must Be Connected Directly:

Room size 31m² – 40m² = 24 000 BTU (7.0Kw)

Room size 41m² – 50m² = 30 000 BTU (8.8Kw)

Room size 51m² – 60m² = 36 000 BTU (10.55Kw)