Advice on Air Conditioning – What Size for What Room

Modern air conditioners are designed to operate quietly. The technology used in the air conditions is so amazing that it cools the area within minutes. When you’re looking to purchase an air condition you must have basic knowledge about this machinery.

The basic technique to buy a new air conditioner is to choose a model that would be best suited to your room based on the floor area so that it would perform proficiently, affordable and steadfastly. The size of the air conditioner matters a lot when you are buying a new one. If you buy an air conditioner which has small BTU capacity for a larger room then you will struggle to keep the room at the contented temperature and if you buy one with large BTU capacity then the room will be ice-cold too quickly without removing enough humidity from the air. When you buy the air conditioner keep in mind that you’ve to select the one which is best suited for your room size. This will help you achieve value for money.

Determine the precise cooling capacity for the room size

With the help of this cooling capacity chart, it would be easy to determine the best capacity according to room’s square footage area. Use the first column to compare your “desired area to be cooled in square meter” and then the second column to select the best fit “Capacity required” for your room. The cooling capacity of an air conditioner has been shown in British thermal units (BTUs) per hour.

The desired area to be Cooled in square meter

Capacity required (BTUs per hour)

30 up to 45


45 up to 75


75 up to 90


90 up to 105


105 up to 120

120 up to 135


135 up to 165


165 up to 215


215 up to 305


305 up to 365


365 up to 425

425 up to 455


455 up to 610


610 up to 760


Match Air Conditioning to Your Room Size

Here is the list of various factors should be taken into consideration in order to find the right air conditioner:

  • Ceiling height
  • Room size
  • The size of windows
  • Insulation
  • The level of sunlight

A guide to required cooling capacities across the range of room sizes is discussed below.

Measuring a room for the right size

The simple method to measure the area of the room is to multiply the width (W) by the length (L) for example; 5m X 3m = 15 meter square

On average for insulated Ceiling 140 watts per sq. meter are required whereas for Uninsulated Ceiling 150 watts per sq. meter are considered as the best fit.

Therefore for a room of 15 meter the calculation for best air conditioner would be 15m X 140 Watts = 2100 Watts

At least 2100 Watts are needed to cool this room. So 2500 W or 2.5 KW air conditioner is perfect for this room. An air conditioner less than 2100 W would perform inefficiently and not cool the room.

The above calculations are suited for the weather patterns in Sydney, Perth, and Brisbane. If you live near the equator the multiplier figure will increase in that case, for example the room of the same size in far north Queensland 15 meter square X 180W = 2700 W would be used.

Room and air conditioner sizing guide

The guide given below can be followed in order to determine the approximate KW range best suited to the room size in which you want to install the air condition.


This size of air conditions is right for most of the small Australian rooms like the study room, small lounge, and small kitchen. Also, this size is totally adequate for 80% of all Australian household bedrooms.


The 3.5 KW air conditioner is ideal for installation in the large master bedrooms or bedrooms with en-suites. This size of air condition would also be suited for small rooms with high ceiling, small size lounge, mid-size kitchens, study and Offices


This air condition can be installed in mid-sized rooms with high ceilings, mid-size lounges, study rooms, large kitchens, and offices. Also, this size of an air conditioner is suitable for large bedrooms or bedrooms with en-suites as well.


Between 7KW to 8KW air flow range is really substantial and an 8KW would only be suited for taking effect in a large open area like large lounges, shops, wide space offices and large open plan areas. If you are planning to use a large air conditioner for two small area parted by a wall it is more ample to use a 7KW for that.

As for 8KW+, it is a very power machine system which is best suited for large open areas where the circulation space is sufficient for the machine to work properly. 

Adjust as necessary

  • Make the adjustments which suit perfect as per your room conditions and look for the circumstances mentioned below:
  • If your room remains deeply shaded then reduce capacity by 10 percent.
  • If your room stays sunny, raise capacity by 10 percent.
  • If the room is occupied by more than two or more people then increase 600 BTUs for every additional individual.
  • If the air conditioner is mounted in a kitchen then add the capacity by 4,000 BTUs.
  • It depends on where you install the unit. If you are mounting the AC near the corner of your room, you need to select the AC unit that would provide the airflow in the desired direction

When it comes to selecting an air conditioner for your room, choosing the correct size of the air conditioner is the most important part of the buying process. While selecting an air conditioner the most common mistake people make is purchasing an underpowered unit which results in improper cooling of the room and over exertion of the machine. Whereas, choosing an oversized air conditioner will definitely cool the room quickly but its inefficient cycle would cost you extra money. Thus, knowing the proper measurements of the room and calculations in KW will help you a lot in making a decision for your next air conditioner. However, it is of equal importance to get a professional HVAC or air conditioner installer or licensed electrician from Service Today for the installation of your AC unit. Doing so will determine that your air conditioner warranty does not get void, the unit gets proper power supply and you get the maximum benefits out of your AC unit. Don’t miss to read our guide on cleaning your Air conditioner