top of page
  • Writer's pictureKennedy Air Conditioning

How to Calculate the Size of the Central AC You Need

When looking for a central air conditioning unit for your house, it's essential not just to go for the first thing you see! The size of your AC unit is vital to how efficiently it will work within your house.

How big your central air conditioner is will be affected significantly by where you plan to put it, as well as the size of your room! Air conditioners use a measurement system of BTU, or British Thermal Units. Any air conditioner will need at least 20 BTU to cool each square foot of your home; however, factors such as ceiling heights and windows may mean you require more BTU for your home.

Why is Size so Important?

We've established that having too small of a unit will mean your house isn't being cooled properly, so often, people go for the biggest AC unit they see regardless of the size of their house. Surely the biggest air conditioner is suitable for any home, right?

Not necessarily. If your air conditioner is too large, it will inevitably begin to 'short cycle', making it turn off and on too much. This will significantly decrease the longevity of your central unit.

How to Calculate the Right Size Unit for You

Calculating the correct BTU for your house is not as stressful as it seems! The average house requires around 12,500 BTU for the central heating unit, but to get a perfect size, you will have to calculate the square footage of your home.

Once you know your entire home's square footage, there are other variables to consider before you make your calculation. The country/state you live in can affect how much power you need. For instance, if you're in a cooler area, you may opt for slightly less BTU than someone in a hot air area since your unit will be doing less work to keep your house cool.

Once you have your square footage and have considered the humidity of your area, you are ready to calculate the size you need! Simply multiply your home's total square footage by 20, then divide it by 12,000. If you live in a cooler climate, subtract one from your answer, but don't do this if you live somewhere warm.

You will be left with the number of tons required for your AC unit. These correspond with Btu units. For instance, 1.5 tons is equivalent to 18,000 BTUs, whereas 5.0 tons is 60,000 BTUs.


Always make sure you have calculated the correct size for your central AC unit so that you don't have any problems crop up along the line! Then, simply calculate the entire square footage of your house, determine whether you are in a cooler or hotter climate, and then get to calculating with the formula outlined above!

This formula is tried and tested by AC professionals and will be sure to guarantee that the central AC unit you buy for your home is the correct size.

168 views0 comments


bottom of page