How to Calculate Air Conditioning Needs
Calculating the air conditioning needs of a particular room is not overly complicated, but is essential to correctly cooling the confined space. There are a variety of factors to take into consideration, but the most important are room size, number of windows and normal room occupancy.
Things You Will Need
 Pencil
 Paper
 Calculator
 Tape measure
With these three vital pieces of information and a little knowledge about the British Thermal Unit, or BTU, you can quickly and easily calculate the air conditioning needs for any room in your house.

Measure the room's width and length in meters. Multiply the length by the width, and then multiply that number by 337 to get the BTUs required to cool that space. For example, 10 meters x 10 meters x 337 = 33,700 BTU.

Measure the windows in meters. Multiply the length and width of the windows together, and then multiply by 870 if they are south facing or 167 if they are north facing. Add the BTU for all of the windows together. For example: .5 meters x .5 meters X 167 (north facing windows) = 41.75 x 3 windows = 125.25 BTU.

Determine the average occupancy of the room. Multiply the normal number of occupants by 400. Example: 3 people x 400 = 1200 BTU.

Add the outcomes of Steps 1 through 3 together to get your total required air conditioning needs for that one room in your house. Pick an air conditioner that can handle the number of BTUs you calculated or more. For example, 33,700 + 125.25 + 1,200 = 35,025.25 BTU required.
Tip
If given the choice, pick an air conditioner that can cool about 10 percent more BTU than what you calculated to take into account common error with regards to the calculations and the actual requirements.
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Tips
 If given the choice, pick an air conditioner that can cool about 10 percent more BTU than what you calculated to take into account common error with regards to the calculations and the actual requirements.
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