How to Size a Window Air Conditioning Unit Cooling Capacity

By | June 3, 2023

How to Size a Window Air Conditioning Unit
Getting the right size window air conditioner for a room is necessary; otherwise, it may not cool the room completely.

  • If a unit is too small, it will not cool the room, and a unit will run constantly.
  • If a unit is too big for a room, it will quickly cool a room and shut off, which can run up an electrical bill.

Air conditioners use the most power when they startup, which makes an oversized unit use more electricity since it is starting and stopping.

An undersized unit will constantly run and never shut off, which will also run up an electrical bill.

Having the correct window unit for a room will make it start and run for the right amount of time, cooling a room the best possible way.

What Is the Right Size Window Air Conditioner Unit for You?

All air conditioners use BTU (British Thermal Units) to measure the amount of cooling power they have.

The square feet a room has is all the information needed to get the right sized window unit.

To get the square feet of a room, simply multiply the width by the length.
How to Size a Window Air Conditioning Unit pic 2
For example, a room 10 feet wide by 15 feet long would be 150 square feet.

To get the BTUs needed, divide the number by .05, which will give the size needed for the room.

For example, the 10 X 15 = 150 square feet.

150 / .05 = 3,000 BTUs
How to Size a Window Air Conditioning Unit pic 3
One thing to keep in mind while sizing a unit is other factors such as how well insulated the room is; doors are constantly being opened, how hot does the outside temperature gets, and so on.

Most will find that a slightly bigger unit is needed.

Window Air Conditioner Cooling Capacity Sizing Chart

100 to 150 Sq Ft5,000 BTUs
150 to 250 Sq Ft 6,000 BTUs
250 to 300 Sq Ft 7,000 BTUs
300 to 350 Sq Ft8,000 BTUs
350 to 400 Sq Ft 9,000 BTUs
400 to 450 Sq Ft 10,000 BTUs
450 to 550 Sq Ft 12,000 BTUs
550 to 700 Sq Ft 14,000 BTUs
700 to 1,000 Sq Ft 18,000 BTUs
1,000 to 1,200 Sq Ft 21,000 BTUs

Getting the right size window air conditioner for a room can be critical to get the best cooling for the lowest running cost. While on paper, simple math will give a rough idea in the real world, other factors need to be taken into consideration.

For example, a kitchen will need a bigger unit to help dissipate heat or a room that is poorly insulated.

Often it can take a bit of trial and error for most with the above generalization.

When buying a unit keep in mind, the efficiency rating and other factors such as how quiet a unit is also playing a role.

Have you had any issues sizing a window air conditioner? Let us knwow your thoughts below.

Category: window mounted air conditioner

About Aaron H. Benetti

Aaron H. Benetti has worked in the HVAC field since 1991. He began his career as an HVAC installer and later began doing troubleshooting and repairs. Around 2010, he began to write books on HVAC topics, mainly tutorials and how-to information. Currently, Aaron writes many articles and posts for websites as well as books and videos on HVAC topics.

2 thoughts on “How to Size a Window Air Conditioning Unit Cooling Capacity

  1. Darlene Biggs

    I need instructions on how to get the right size and condition of for my window for to fit in my window not the square footage to cool walk the world


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