Window Air Conditioning Sizing – Size AC Unit In BTUs

Do you know the correct size window air conditioning unit to buy for your room or home? If a window air conditioning unit is not the right size for the space it is in, it won’t work efficiently. AC units need to be sized correctly in BTUs to cool a room. If the AC unit is too small it will never adequately cool that space. Find the window air conditioner size chart below to help you find the exact BTU sized AC unit needed to cool your room.

window ac size chartWindow AC Size Chart in BTUs

Buying a suitable sized window air conditioner is key to cooling your room. Window AC sizing is done by looking at how many BTUs the AC unit can produce vs the square footage of your room.

  • Window AC units are most effective when the window unit is large enough to cool the room it’s placed in.
  • A window AC unit that’s too large for a room will cool the room very quickly and shut off often therefore making your electricity bill excessively higher.
  • The window AC unit that’s too small for a room will not cool the room and will never reach the proper temperature causing the AC unit to constantly run and cause higher electric bills.
  • Air conditioners use the most energy when they initially start up, which makes oversized units a bad idea as they will start and stop excessively in a smaller room.
  • A correctly sized window Aircon or AC unit for a room will enable it to start and run as needed, cooling the space to the set temperature and without constant starting and stopping.

What Size Window Air Conditioner Do I Need?

Air conditioning units use BTUs to measure the cooling capability they have. The square footage or size of a room is the most important factor in choosing an air conditioning unit.

To find the square footage of the room the AC will be in, multiply the width by the length of the room.

Example: A room 20 feet wide by 18 feet long would be 360 square feet.

To find out the BTUs you need for proper sized cooling divide the number by .05 and this will give you the BTU size you need for the room. Use a calculator to find out your square footage. Take the square footage of your room, in this example 360, and divide by .05. This math will give you the number 7200.

The number 7200 is the amount of BTUs the room needs to properly cool it. In this example, you would want to find a window AC unit that is 7200 BTUs or larger. If the room is not insulated well, large windows with sun coming in, or doors are left open, you may need to go for a larger BTU AC unit.

find out window AC size needed in BTUsFind window AC size needed in BTUs

Window AC Sizing Chart

100 to 150 Square Feet = 5,000 BTUs

150 to 250 Square Feet = 6,000 BTUs

250 to 350 Square Feet = 7,000 BTUs

350 to 400 Square Feet = 9,000 BTUs

400 to 450 Square Feet = 10,000 BTUs

450 to 550 Square Feet = 12,000 BTUs

550 to 700 Square Feet = 14,000 BTUs

700 to 1,000 Square Feet = 18,000 BTUs

1,000 to 1,200 Square Feet = 21,000 BTUs

To get the best cooling for a given space, you should first determine what size (amount of BTUs) type of air conditioner to purchase. Window air conditioning units can be difficult to size accurately because of the assorted factors involved.

Other factors for which window AC unit to get for the room would be the energy efficiency of the unit, how noisy is the unit, the price of the unit compared to other units with the same BTU rating, and factors such as ceiling height and how much sunlight comes into the room you are wanting to cool. Consider all these factors and you will get the best size window AC for the room you need too cool down.

Once you know the BTU needed to cool your room, you will need to measure the window the AC unit will be installed in and be sure it will fit. Most window ACs come with a kit to install the AC in the window to fit securely.

Use the math we described above to get the best estimate of BTUs needed.

Remember, window AC size is not done by how large the AC unit is physically, it is figured out by how much cooling in BTUs the AC can produce. One type of window AC unit may be physically larger in dimensions, but may produce less BTUs then a smaller unit.

This page is meant for sizing a window AC unit to the square footage of the room to cool properly in BTUs. This page is not meant for finding the actual physical dimensions of the window AC itself. This is a “How many BTUs does my window AC need to have to cool my room?” information.

MORE WINDOW AC HELP: Room is hot with window AC runningWindow air conditioner cools then quickly turns offWindow AC stopped working

If you need help finding out which window AC BTU rating is best for your particular room conditions or have questions with a window AC not working, please leave a comment below and someone can assist you.

ALLEN VETTER - DIY Repair Assistant
Allen is a Home Maintenance/Appliance Tech and the author/creator of this website. He has 33 years of experience troubleshooting and repairing all types of appliances. Contact here

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