Your air conditioner size is an important part of its performance. If your AC isn’t cooling adequately (too small?) or if it is making your home cool and clammy (too big?), knowing the size will tell you if size is part of the problem or if you should look to other factors.

Other homeowners will want to know how to tell tonnage of ac unit if they’re planning to replace it. Knowing AC size helps with budgeting for a replacement air conditioner.

## Where to Find the Ton Rating of Your Air Conditioner

Let’s see out how to find how big your air conditioner is.

**Buying an Air Conditioner?** If you have just bought a whole house AC unit, or are shopping for one, the size of the air conditioner should be listed right on the box or crate. It might tell you the actual size in tons, in BTU’s, or both. But now you know how to convert the BTU size to tons, right? Just divide the BTU number by 12,000. An AC unit rated at 24,000 BTU’s is 2 tons. A unit rated at 42,000 BTU’s is 3.5 tons, and so on.

**Already Have an Air Conditioner?** But if you are trying to find out how many tons is the air conditioner that is already installed in your home, there is another way. You must go outside to the condenser unit. This is a large, box-shaped unit that has louvers on the sides and a wire grille on top. It’s usually about waist high. Look around the back or on the side of the unit, and you should find a label with a lot of information on it.

Find the model number on that label and within that number you will see two digits that can be divided by 12. They are usually toward the end of the model number and will be 24 or 30 or 48 or another number like that. Divide this number by 12 to get the tonnage of your AC unit. Most homes will use an air conditioner that is between 1 and 5 tons. Here are the numbers that you will probably see and the tonnage they represent:

- 12 = 1 ton (Rare. Most lines of condensing units start at 1.5 tons)
- 18 = 1.5 tons
- 24 = 2 tons
- 30 = 2.5 tons
- 36 = 3 tons
- 42 = 3.5 tons
- 48 = 4 tons
- 60 = 5 tons

Here are a couple of examples of model numbers. See if you can tell how many tons they are.

- Rheem RA16 model number RA1624AJ1NB
- American Standard Platinum 18 model number 4A7V8060A

If you determined that the Rheem model is 2 tons (using the 24 in the model number), you are correct. The RA16 at the beginning of the number is the model, the RA16.

The American Standard unit is a little trickier, but it’s a 5-ton AC. The “80” might be confusing, but the clue is that the largest residential air conditioners are 60,000 BTUs, so “80” would be too large.

If you look at either this Rheem page or this American Standard page, you’ll see a whole range of sizes for each of the AC models.

**Keep in mind:** Dividing the correct number by 12 will always produce a whole number or a “.5” number.

### If You Have a Heat Pump

Your home air conditioning may come from a heat pump which does double duty; it cools in the summer and heats in the winter. The outdoor condenser unit will look just like an AC unit. It will have a label on the side or back, and the same two digits in the model number are what you are looking for. Just divide by 12 and you will know how many tons your AC unit is.

## How Many Tons is My AC Unit?

Good question, but why should I need to know?

It’s important to know the tonnage of your AC unit because it will tell you if you have the correct size for your home, apartment, condominium or other dwelling. The ton rating of an air conditioner is the measure of how much heat it can remove from a home in one hour. That’s what an air conditioner does; it removes heat from your living space and transfers it to the outside environment. The net result is a home that is cooler inside than it is outside.

The history of the science behind this is rather interesting. It was the result of some tests done during the late 1800’s. They were trying to determine how much heat it would take to melt one ton of ice in 24 hours. They came up with the fact that it took about 12,000 BTU’s to accomplish this. “BTU” stands for British Thermal Unit, which has been a standard for measuring heat for a long time.

So, putting the numbers together, it was established that one ton of air conditioning can remove 12,000 BTUs of air in one hour. This is how all air conditioning units are rated today. Smaller units, like window air conditioners, are simply given a BTU rating, usually between 8,000 and 15,000 BTUs. Larger units, like those intended to cool an entire building, are rated by tons. A 1 ton AC unit can remove 12,000 BTUs of air in an hour. A 3 ton unit can remove 36,000 BTUs per hour, and so on.

The reason it is important to know how many ton is my AC unit is because it will determine how efficient the AC unit is. If it is too small for your home, it will run a lot, but not be able to cool it very well when the weather gets hot. Result: a large electric bill, but a home that is not comfortable. If it is too large for your home, it will cool it too quickly and shut off before it has removed moisture from the air inside. Result: a cool, clammy home.

## What Size AC Do I Need?

Now that you know what a ton of air conditioning can do, and why you need the correct size unit for your home, here is how to determine what size your AC should be for your home.

According to the US Department of Energy, for an average home with normal ceiling heights and window sizes, it will need 1 ton of air conditioning for every 600-750 square feet of building area.

This can vary depending on the climate zone in which you live, and how well your particular home is insulated.

So with this as a reference, if your home is around 1200 square feet in size and in a moderate climate, you will need an AC unit of 1.5 to 2 tons. If it is 2500 square feet, it should be a 3.5 to 4 ton unit.

We have developed this AC Sizing Calculator which take more factors (climate zone, insulation and sun exposure) into consideration. You can get a more accurate size now:)

Another factor to consider is the SEER rating. They usually run between 13 and 22. The higher the SEER rating, the more efficient the system will be. If the unit is Energy Star rated, that is even better.