BTU Calculator: What Size Air Conditioner Do I Need?

When you're shopping for a new air conditioner, finding the best BTU level for the soon-to-be-cooled room is a very important step. We've got some answers to common air conditioner questions, plus an AC BTU calculator to allow you to figure out the best possible air conditioner size!

• What if I use too low of a BTU for the room size?
• What if the BTU Rating is too high?
• What's the best BTU calculation formula for an air conditioner?
• How do I measure square footage of a room?
• Do I need to do anything differently for a portable AC?
• I've measured my room's area and ceiling height, and I'm ready for the BTU calculator!
• What are some other factors that may impact the size of air conditioner I need?

What is BTU in an AC?

A BTU, or British Thermal Unit, is the amount of energy needed to raise 1 pound of water by 1 degree Fahrenheit while at sea level. When it comes to air conditioners, the BTU rating tells you how many BTUs per hour the machine can remove from the air. The higher the rating, the more high-intensity the cooling.

What if I use too low of a BTU for the room size?

If the air conditioner is too small for the room, it can't bring the room to a comfortable coolness level. The unit will be running constantly without hitting the proper temperature or dehumidification levels, making it extremely inefficient and costly.

What if the BTU Rating is too high?

In order to create a comfortable temperature, an air conditioner must be able to dehumidify the air as well as cool it. Using an air conditioner that's too big for the room will result in it shutting off early without allowing the space to properly dehumidify, and the excess moisture will create an uncomfortably damp environment.

What's the best BTU calculation formula for an air conditioner?

Simply measure the room's square footage and ceiling height, plug it into our BTU calculator, answer a few other questions, and your answer will appear!

How do I measure square footage of a room?

To calculate a room's area in square feet, simply multiply its length by its width. For instance, if the room is a rectangular 10 feet by 20 feet, the area would be 200 square feet. If the room is a perfectly-square 20 feet by 20 feet, the total area would be 400 square feet. Don't worry about factoring height into this equation - it'll be a separate measurement on our air conditioner BTU calculator.

Do I need to do anything differently for a portable AC?

Portable air conditioners were originally labeled with the same BTU rating system as window and through-the-wall air conditioners, and it wasn't until recently that manufacturers realized this led to an inaccurate assessment of the unit's cooling capabilities. Unlike a window or wall unit, a portable air conditioner sits entirely inside a room, and the emitted heat ends up dissipating into the very space it's trying to cool. This means the room wasn't getting as cool as the portable unit's BTU rating indicated. Today's updated BTU system means a more accurate rating, called the DOE rating, will be included in the product specs. This means you'll get a more accurate idea of the cooling capabilities, making it easier to find the perfect unit for your home.

What are some other factors that may impact the size of air conditioner I need?

There are a few additional things that should be taken into account when it comes to the BTU calculations.

• Sun Exposure and Number of Windows - If the room is generally exposed to a lot of sun, the resulting warmth may require an AC with a higher BTU.
• Number of People in the Home - A greater concentration of people will result in a warmer room that will need more cooling power.
• Appliances or Electronics in a Room - When determining BTU level for your new AC, be sure to factor in heat from electronic equipment, or from appliances like cooktops or ovens.

I've measured my room's area and ceiling height, and I'm ready for the BTU calculator!

Excellent - scroll to the top and get started!