Air Conditioner Calculator

Updated May 16, 2019

What size air conditioner do you need for your property? This is a fundamental question that needs to be answered if you are looking for a new ac unit for your residential or commercial property.

Installing an air conditioning unit that is too large can result in a home becoming too cool, too fast, while installing a unit that is too small can result in your home never reaching the preferred temperature and moisture levels.

Therefore, in order to determine the right size air conditioner for your property, you can use an air conditioner calculator for guidance. By no means is this the only metric you should take into account, it can certainly help to provide you with an estimation.

BTU Calculator for Air Conditioning

Choosing the right size air conditioner involves what is referred to as the load calculation. This is a calculation that takes into account both the British Thermal Units (BTUs) and the tonnage rating of the air conditioner.

British Thermal Units (BTUs) is defined as the amount of energy needed to cool or heat one pound of water by one degree Fahrenheit. In the context of air conditioners, the BTU refers to the amount of heat the unit can remove from a certain space, typically measured in square feet.

The tonnage is a rating given to an air conditioner and refers to the amount of heat the unit can remove, for example, a 1-ton air conditioning unit can remove 12,000 Btu, or British Thermal Units, of heat per hour.

AC Tonnage Calculator Per Square Foot

The above calculator will help you determine the right size air conditioning unit you require to help keep your residential property cool and comfortable. The above calculator will provide an estimation of the required BTUs for the majority of residential living spaces.

However, it should not be used for commercial or whole house installations – it is appropriate for providing an estimation of mini-split, through-the-wall, PTAC or sliding window AC size.

Once you have determined the number of BTUs you require, you will need to select an air conditioner at the correct tonnage to remove the heat. For instance, each ton of air conditioning can remove 12,000 BTUs from a building per hour.

In order to work this, you can plug the numbers into this very simple equation:

There are 12,000 Btu’s per ton.

Therefore, if you require 24,000 BTU’s:

24,000 Btu’s/12,000 Btu’s per ton = 2 tons.

If you are replacing a model already installed in your home, you can also use the same equation to figure out its size and therefore skip using the calculator above. Often, the model number found on the air conditioner will indicate it’s BTU rating.

For example model, HDZ120241K is a 2-ton unit, since the 24 digits represent 24,000 BTUs.

What Size Central Air Conditioner do I Need? 

As previously mentioned, the correct size air conditioner for your home mostly depends on the square foot of your property and ceiling height. However, other factors do come into play, this includes your local climate, the amount of sun exposure and the current state of your properties insulation.

Therefore, you ought to be aware that the above calculator is for estimation purposes only and assumes that you live in an average sized property with all of the typical features. In order to get a make a more accurate size decision, many people choose to have a professional HVAC technician carry out a Manual J calculation.

A Manual J Calculation is an industry-accepted procedure for cooling load calculation. It is far more accurate since it takes into account a multitude of different factors and so can be used to determine AC sizing for both commercial and residential properties.

The following is an example given for a standard room with 8-foot ceilings (roughly 20 BTU for each square foot):

  • 8,000 BTUs will cover 200 sq. ft. (1,600 cubic feet)
  • 10,000 BTUs will cover 300 sq. ft. (2,400 cubic feet)
  • 12,000 BTUs will cover 400 sq. ft. (3,200 cubic feet)
  • 13,000 BTUs will cover 450 sq. ft. (3,600 cubic feet)
  • 14,000 BTUs will cover 500 sq. ft. (4,000 cubic feet)

Commercial Air Conditioner Calculator 

As you might have expected the sizing of an ac unit for a commercial building is quite different from residential sizing. As airconwa.com.au suggests commercial properties such as warehouses typically have much higher ceilings and floor area. In fact, there is so much variation between commercial buildings that it’s almost impossible to use standard estimations.

Commercial Air Conditioner Rule of Thumb 

In order to estimate the correct size ac, you require for your commercial building you can use a similar method as the residential equation above. First, calculate the area of the space you want to cool (width of the room x length of the room).

Next, you divide the square footage by 500 and then multiply the number by 12,00 to get the total BTUs you require to cool the space. For instance, a 9,000 square foot space divided by 500 equals 18. Next, multiply 18 by 9,000 to get 216,000 BTUs.

Remember to add an additional 380 BTUs for everybody that will reside in the space, use an average if this will change. Also add an additional 1,200 BTU for each kitchen space too.