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Are you planning to shop for an air conditioning unit anytime soon? You’ll want to understand how to calculate the right size in order to get a unit with the capacity to give you some much-needed cool air. However, there are lots of things to consider when it comes to this topic.


You’ll want to keep in mind that when people talk about size in reference to AC units, they aren’t actually referring to the physical dimensions of the appliance itself, but rather the cooling capacity which is measured in Thermal Units. Whether you are planning to get a window AC or a central air unit, choosing the right size based on the area that needs cooling will give you the best efficiency, which is also extremely necessary to lowering your operating costs and lower your utility bills.


Below are some detailed steps to help you decide on what size AC unit is best for your home and the area that needs cooling.


Calculate the Size of the Home Space(s) That Will be Cooled

For most efficient cooling, whether it is rainy, moist, hot, or it’s humid out, you’ll need to get the size of the home or area where the AC unit is going to be installed. Below are the simple steps on how to do so.


  1. Multiply the the length times the width of the room or area to be cooled.
  2. Multiply the answer by 25 BTU.




The room is 12 ft. wide and 15 ft. long. To get the area that would be:


12×15= 180 sq. ft.


Get the BTU cooling capacity needed by:

180 sq.ft x 25 BTU = 4,500 BTU


So for a 180 sq.ft room, you need an air conditioning unit that has a 4,500 BTU cooling capacity

Frequently asked questions


  • Will a smaller air conditioner work just as well as a larger one?


Air conditioners with smaller BTU units will have to continually run to be able to keep up with a larger rooms cooling needs. This means higher electric bills and lower energy efficiency. Moreover, the unit will not be able to cool the area or your room the way you want it to or as quickly as you’d like, in most cases.


  • Is it better to use a larger AC unit?


An air conditioner that is too can large can be, more or less, overkill. It is true that a larger AC unit may cool the area more quickly, but you’ll probably lose all the gain with loss from the energy and space it is consuming.


There are other things, too. Like humidity. Even though the air is cooler, if your AC doesn’t run long enough because the big unit can cool the room so quickly, it won’t be able to extract the moisture from the air properly. Uhoh! In addition, an air conditioner unit that is too large will cycle on and off more frequently and this can lead to a shorter lifespan for your AC unit and other issues down the road.


Do yourself a favor and measure the area that needs to be cooled by calculating its BTU.

Find out the cooling options that best fill the needs of your home and choose the right size air conditioner unti without regrets. 


Need help installing or doing some maintenance on your HVAC? We are a skilled team of heating and cooling technicians that can help you no matter the problems you’re facing. Give us a call TODAY for more information!