How To Find The Proper Aircon Capacity For Your Room Size

Choosing the right aircon capacity for your room size will have a big effect on your comfort and your electricity bill. If you choose a unit that is too small, it won’t cool your room quickly and efficiently; too big, then it will cool too quickly without removing the humidity – making you cold and clammy.

Here is a quick guide to help you find the proper aircon capacity for your room size:

How aircon capacity is measured

An air conditioner’s cooling capacity is measured in either kilojoules/hour (kJ/hr) or British Thermal Units (BTU). This is used to measure the amount of heat your aircon can remove from the air per hour of use.

In the Philippines, we mostly use kJ/hr so we will use this for our calculations.

What about horsepower (HP)?

Aside from kJ/hr and BTU, an aircon’s capacity can also be measured in horsepower (HP). However, HP is used to measure the motor’s power, not the aircon’s cooling capacity.

A unit with the same horsepower rating may differ in their cooling capacity. Therefore it is much more accurate to use kJ/hr than HP when calculating the capacity of your aircon.

It’s not totally useless though, as you can use it to filter the models that you will canvass. Keep in mind that 1.0HP = 9,495 kJ/hr.

Aircon capacity to room size guide

An air conditioner’s recommended floor area is measured in square meters (sqm or m2). If you have your house’s floor plan, this will be easy. Otherwise, grab a tape measure and measure the room’s length and width and multiply both numbers to get the room’s size in sqm.

To get a rough calculation, multiply your room size by 500. So if your room is 10 sqm. in size, you need an aircon with 5,000 kJ/hr of cooling capacity – which most 0.5 HP window type aircons have.

Use this chart to get the baseline capacity:

Room SizeCapacity
HP Rating
≤ 10 sqm.5,0000.5 HP
10 – 15 sqm.5,000 – 7,5000.75 HP
15 – 19 sqm.7,500 – 9,5001.0 HP
19 – 25 sqm.9,500 – 12,5001.5 HP
25 – 35 sqm.12,500 – 17,5002.0 HP
35 – 43 sqm.17,500 – 21,5002.5 HP

Again, this is only a baseline. There are other factors that we need to account for other than just the room size.

Other factors

Using your room’s required cooling capacity as a baseline, adjust your calculations depending on the following circumstances:

  • If the room is sunny – add 10% to the room’s cooling capacity
  • If the room is shaded subtract 10% to the room’s cooling capacity
  • Number of occupants – if the room is used by more than two people, add 633 kJ/hr for each additional person.
  • If you cook in the room – add 4,220 kJ/hr. This is mostly applicable for people living in a studio type room.


Given: 20 sqm. room, with 3 occupants. The room also has a lot of windows to let the sunlight in.

Formula: ((room size x 500) + additional occupant) * 10%
((20 x 500) + 633) * 10%
10,633 + 10%

Required cooling capacity = 11,696.3 kJ/hr

Recommended model size: 1.5 HP

When in doubt…

While this can get you a good estimation of the proper aircon capacity for your room, it will always be better to consult an authorized installer to perform a site survey to give you the most accurate calculation.

Most brands and third-party installers offer this service especially for split type air conditioners. However, you should also calculate on your own so that you’ll both be in the same page.


Bigger is not always better. If the aircon is too large, it will use up more energy, take away less humidity, and will have a higher wear and tear compared to the proper-sized models.

Smaller is not ideal as well. A small aircon will struggle to cool bigger rooms, which will use up more energy, and will strain your unit’s motor.

With this method of calculation, you can gauge accurately where the sweet spot is. If you’re not confident with finding this Goldilocks zone on your own, don’t hesitate to call a professional!


1 thought on “How To Find The Proper Aircon Capacity For Your Room Size”

  1. Identifying the proper aircon capacity for your room help you to choose the bet air conditioner to provide better cooling for you room. The information that you have shared it with us will help us in doing that better. Thank you for sharing it with us.


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