What Does BTU Mean for an Air Conditioner?

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Updated September 22, 2022

Many people simply purchase an air conditioner and let it rip. However, to make sure you buy the absolute best air conditioner for your home, it is essential to familiarize yourself with some HVAC jargon. Below, we will be explaining the question: what does BTU mean for an air conditioner, and how does it relate to your home cooling situation?


  • BTU stands for British Thermal Units and is a way of measuring the overall cooling power of air conditioning systems.
  • Overall, BTU measurements need to be calculated to fit the square footage of your room or house.
  • To measure for proper BTUs, calculate the total square feet by 20 to get a rough estimate.

And if you’ve already bought an air conditioner and need to see if it’s the right size, we have another article that explains how to find out the BTUs on your air conditioner.

What Does BTU Mean for an Air Conditioner

The term BTU stands for “British Thermal Unit.” What this acronym represents is a measurement of energy. No one knows where the term came from, but famed mathematician and physicist, James Prescott Joule, popularized it as a measurement.

Insider Tip

A great way to ensure you aren’t overspending on AC energy is to change or clean the unit’s air filter every 90 days.

Formally, BTU is defined as “the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.” But in the practical world of AC, where the unit calculates how much heat is removed instead of created, the BTU is more simply used to measure a unit’s power. So, when it boils (or cools) down to it: more BTUs, more power.

Additionally, if you’re looking for more educational resources on air conditioners, check out some of our articles covering what do air conditioner symbols mean and what does P1 mean on an air conditioner?

How Many BTUs are Necessary?

The appropriate amount of BTUs depends on a variety of factors, such as a home’s square footage, ceiling height, direct sunlight, quality of insulation, and floor plan. All that being said, it’s vital to know what the right size air conditioner is for your home because it will affect energy bills.

Remember that this applies to all types of air conditioners, whether a window, portable, or central unit. And for those looking for AC units to fit in small spaces, we also have an article covering what a casement air conditioner is.

Larger spaces require greater cooling capacity and power, which means more BTUs. There’s an EPA-recommended formula that says you should have 20 BTUs in cooling power for each square foot of living space. However, keep in mind that you will also need to adjust for the specific things stated in the above paragraph. And, if in doubt, you can contact an HVAC repair service to measure for you.


An AC unit won’t efficiently cool space if its BTU rating is too high for the square footage. It’ll also raise your energy bills.

Below are a few general BTU ratings for different-sized rooms:

  • Bedroom/Office (100 to 250 sqft.) – 5,000 – 6,500 BTU
  • Large Bedroom ( 250 to 350 sqft.) – 7,000 – 8,500 BTU
  • Living Room/Studio Apartment (350 to 550 sqft.) – 9,000 – 12,500 BTU

Finally, if you want to read an article that explores a similar question, check out our article that addresses what to do if an air conditioner’s tonnage is too small.

STAT: If you have high ceilings, you’ll have to add another 10% to the total necessary BTUs. (source)

What Does BTU Mean for an Air Conditioner FAQs

Do more BTUs automatically mean more cooling power?

While you will have more cooling power, it's always better that an air conditioner's BTU rating matches your living space. Too many BTUs will lead to higher than necessary energy bills.

What does tonnage mean?

Tonnage is an HVAC term used to express how much heat can be removed from a home in one hour.

What if you have too few BTUs?

Having too few BTUs likely means you'll never be able to achieve the correct temperature and that the AC will constantly be running.
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