What size window air conditioner unit do you need? This estimator will help you assess the right model for your room.


Cubic area of room to be cooled: Direction the room faces (choose one) North South East West Condition of your insulation (choose one) Good Fair Poor Number of BTUs recommended:

Please note: For your convenience, this calculation has been rounded up slightly.

Important reminder: Every effort has been made to ensure the accuracy of this calculation. But before purchasing materials for any project, please check amounts with your suppliers or contractors.

Helpful Information

When choosing a window air conditioner, don't assume that buying the most powerful model is the best choice. An air conditioner that is too powerful for the room will not remove enough humidity, because it cools too quickly. And of course, a model that is too weak will fail to make a room comfortable. The cooling power of an air conditioner is calculated in British Thermal Units (BTUs). (One BTU is enough energy to heat one pound of water by 1 degree F.)

A few tips: If you need to install a unit that delivers 12,000 BTUs or more, have an electrician install a 240-volt receptacle. Smaller units can be plugged into a standard 120-volt receptacle, but make sure that by doing so you will not overload the circuit (see our Circuit Load estimator).

Other factors to consider: If the room is directly above a room with no air conditioning; if more than three people typically inhabit the room; or if the room's door will often be opened and closed, buy a model approximately 1,000 BTUs stronger than indicated by this calculator.


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