How to Calculate Room Size for AC

Are you not sure what is the right size of an air conditioner according to your house? Are you concerned with the rising electricity charges and do not want to overbear? Then it would help if you found the right tonnage of air conditioner for your room. The good news is, calculating the same is fairly easy, and today that is what the focus is. Hence keep reading if you want to find out the correct AC size for your room.  

Features of an AC you should look out for 

The primary reason you could be looking for the right size and tonnage for your AC is that you want efficient cooling. It is easy to get carried away when buying an appliance that makes your house better. That said, efficiency does not come just by the size; you also need to ensure that your AC has the following features: 

1. Energy star rating 

The BTU provides the energy star. According to this, the higher you go, the more energy you save. These ACs are tested, and only after passing the guidelines are they marked for stars. For instance, if you want a very energy-efficient air conditioner, do not select one which has less than 3 stars. 

2. Smaller features

While you cannot always guarantee maximum efficiency, you can ensure that the AC is being useful to you with its maximum potential. Therefore, please keep a lookout for smaller features that make it perfect for you. These features may include: 

  • Auto Cleaning 
  • Timers and sleep modes 
  • Different sleep profiles 
  • Wifi and voice control 
  • Access to Alexa and Google Assistant.

Now that we have understood how to choose a good AC relevant to your needs. Let’s talk about the most basic thing that is needed for efficient cooling. This is a proper size and cooling capacity for the correct size of the room.

How to calculate the room size for your AC

People often confuse the various sizes and cooling capacities of an air conditioner. In such cases, they go by what the air conditioner salesman is saying to them. However, when buying things online, you do not have a lot of guidance and thus need to be your own master.

To find out what kind of air conditioner will be ideal for you, you must find out the cooling capacity. This will determine the tonnage of AC that will be appropriate for a specific size of your room. To achieve that, you need to calculate the BTU, which can be done in two ways:

1. By area 

Measuring the cooling capacity via area is the most common way of determining the cooling capacity. All you have to do is determine the square footage of the house and multiply it by 25 BTU. Therefore, for example, the length and breadth of the house are 12 and 15 (feet) respectively.

Therefore the area of the room would be 12*15, which is 180 square feet. To understand the BTU cooling capacity, multiply the number by 25, which stands to 4500 BTU. Thus, this is the cooling capacity you will need for your house. For this, the tonnage would be approx. 1.5 tons ideally. 

Use this BTU calculator – 

If you do not want to overcomplicate it, here is a simpler method. All you have to do is calculate the area and divide the square root of it by 10. So, in this case, the area was 180, and the square root was 13.4. Therefore when you divide it by 10, you have 1.3. This is the ideal tonnage of the AC that you should buy.

2. By volume 

Another way to calculate the tonnage of an air conditioner is by volume. Sometimes when the house is filled with people, the temperature rises regardless of the machine working at its 100%. Therefore, it is best to determine the tonnage via the volume of the house. 

Let’s say that the room is 10 feet long and 15 feet wide. The height is 20 feet up. If you calculate the volume of the room, length * breadth * height, you get 10*15*20. This equals 3000 cubic feet. Hence the tonnage of the air conditioner should be 3 tons approx.

Other reasons to get an increased capacity

Sometimes it so happens that the ideal tonnage is not providing enough cooling. Just the room area is not enough to have the perfect machine providing a pleasant temperature. Many other reasons affect the room’s temperature besides the size. Hence if you have any of the following situations in your house, get a slightly higher cooling capacity and volume.

  • If more than five people are living in the house every day 
  • If the window is directly allowing sunlight and heat in the room 
  • If you are just under the terrace 
  • The house you stay in is too ventilated 
  • The room you want to put an AC in is closer to the kitchen. 
  • If you are prone to regular parties in the house

Why do you need a proper tonnage for your house?

Many people are unaware of the reasons for getting an air conditioner with proper tonnage. Lower capacity AC costs less than higher capacity, leading people to buy the wrong volume. They might think that they are saving money, but they are doing more harm on the contrary. Hence to give you a little more clarity, here are some reasons why you should buy the appropriate tonnage: 

If you get a tonnage that is less than what is required, it will take longer to cool the room and carry the heat load. Thus, you will consequently see your electric bills skyrocket. 

On the contrary, you’re mistaken if you think a bigger tonnage will help you more. For example, if you get a 3 ton AC for a 180 square feet room, you may get more cooling. However, the dehumidifier will not work properly and simultaneously. This will result in a soggy feeling in the air. 


Therefore, to sum up, finding the correct tonnage is rather important, and with the easy calculations above, you can determine them on your own. That said, it is best to leave these things to professionals as they would inquire about the number of people present in your home. They will also look into the positioning of the house and the windows to the room and deduce a perfect conclusion that would make your family and your electric bill.

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