What Size Air Conditioner Do I Need?

When purchasing a new air conditioning system, it is important to select a unit that is the right size for your home. So, how do you calculate the appropriate AC size, and what is air conditioner tonnage? Keep reading to find out what size air conditioner you actually need!

Factors to Consider

An AC unit maintained by Shriver Mechanical

When you are trying to determine the size of the AC unit you need there are several factors to consider. First, you must take into account the size of your home – the square footage is one of the biggest determining factors in selecting an appropriate air conditioner. Where you live is also important, as different climates will have varying requirements when it comes to what size air conditioner you need. How many windows do you have, and how big are they? How much sunlight or shade does the home get? The answers to these questions are needed to calculate the right AC size.


The age and quality of the ductwork and insulation in the home will also affect the tonnage required for your new AC unit. If your house is well-insulated and has newer windows that are properly sealed, you may be able to get away with a smaller unit that still meets your other requirements. If this is not the case, you may need to opt for a larger unit to make up for the air that is lost as a result of poor insulation. You also have to be careful not to get one that is too big! If the air conditioner is oversized, it will begin to short cycle – this means that the compressor turns on and off frequently, which reduces the life of the system and increases your operating costs.

How to Calculate Air Conditioner Tonnage

Calculating air conditioner tonnage can help you determine what size air conditioner you need. Tonnage refers to the ability of your AC unit to cool your home, and one ton is equal to cooling 12,000 BTUs in one hour. This is the basic equation for calculating the appropriate tonnage requirements for your home:

[(Home Square Footage x 30) / (12,000)] - 1

In simple terms, you multiply the square footage of your home by 30, then divide that by 12,000. Once you have that number, you subtract 1. For example, if your house is 2,000 square feet, you need a 4-ton AC unit. The calculation would be as follows:


2,000 Square Feet x 30 = 60,000


60,000 / 12,000 = 5


5 - 1 = 4 Tons


While this is the basic formula, some tweaks can be made to adjust for the other factors we discussed earlier. For instance, if you live in a warm region, you will likely need a larger AC Unit – so don't subtract 1 in the last step of the equation. Staying in line with the previous example, you would likely need a 5-ton air conditioner if you live in a hotter, more humid region.


To get a more accurate number, you should enter the length, width, and height of your home into a BTU Calculator. These calculators will also take into account basic insulation information as well as a climate zone map to help you determine what size air conditioner you need.