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Air conditioner size calculator: what kW you need

Estimates the cooling size in kW for one room, using the MHIAA sizing chart and an ActronAir rule of thumb.

Calculator · Updated 15 October 2026

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Enter your room's floor area and pick the room class that fits to see a rough cooling size in kW from two published rules of thumb.

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Pick the description closest to your room.

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Estimated cooling load (MHIAA room class A): 2.0 kW

Estimated cooling load (MHIAA room class A)

2.0 kW

Estimated cooling load (MHIAA room class A)
2.0 kW
Higher-load check (ActronAir guide, 150 W/m²)
3.0 kW
  • MHIAA room class A works out at 100 W/m², derived from the chart's kW per m² (3.5 kW unit ÷ 35 m² maximum floor area). Source: MHIAA Air Conditioning Sizing Chart.
  • The higher-load check is ActronAir's rough rule of 150 W/m² for a 2.4 m ceiling. The two sources differ, so the spread between the two numbers is a fair sign of how rough any rule of thumb is.
  • Both figures are rounded up to the next 0.5 kW. Ceiling height and the number of people are not included.
  • This is a guide only. A licensed installer should confirm the size with a heat load assessment before you buy.
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On this page
  1. The calculator
  2. How this is worked out
  3. Frequently asked questions

How this is worked out

  1. Pick the MHIAA room class (A to D) whose description is closest to your room. The classes cover insulation, windows, shading, direction the room faces and climate.
  2. Cooling load = floor area × the class's W/m², rounded up to the next 0.5 kW. The W/m² for each class is worked out from the MHIAA chart's kW per m² (3.5 kW unit ÷ the maximum floor area it lists for that class).
  3. A second figure shows ActronAir's rough rule of 150 W/m² for a 2.4 m ceiling, also rounded up to the next 0.5 kW, so you can see the spread between the two sources.
  4. Ceiling height and the number of people in the room are not included.

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Frequently asked questions

Can I rely on this to choose an air conditioner?

No. It is a guide to help you ask better questions. A licensed installer should confirm the size, ideally with a heat load assessment of your room.

Why are there two different numbers?

They come from two different sources. The MHIAA chart changes with the room class, and ActronAir uses one rough figure of 150 W/m². The sources differ, and the gap shows how rough any rule of thumb is.

What happens if the unit is too big or too small?

An undersized unit runs flat out and may not keep the room comfortable on hot days. An oversized unit switches on and off more often and may not take moisture out of the air well. Neither is ideal, which is why a proper assessment is worth getting.

Does insulation make a difference?

Yes. Roof insulation is one of the biggest factors in how much cooling a room needs, which is why the MHIAA classes start with insulation, windows and shading.

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Updated 15 October 2026. An estimate is a starting point — compare quotes for the same scope.

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