A conversion exists for BTU to watts, but it does not apply in this instance. Air conditioners are rated by how much heat they can remove from a space in one hour. This rating does not imply they operate at 100 percent efficiency. Power usage requires calculating watts from voltage and amperes. The number of BTUs an air conditioner moves will convert directly to watts if you multiply by 0.293071, but the result is not the same as the power in watts used by the air conditioner. If the air conditioner nameplate includes a power factor specification, multiply watts or kilowatts by the power factor. The result will more accurately reflect the amount of power the electric utility will charge you to operate the appliance.
Manufacturers rate air conditioners on how much heat they can move from inside to outdoors. This rating is given in British Thermal Units or BTUs. A 5,000-BTU air conditioner moves less heat than an 8,000-BTU air conditioner, but the larger unit will use more electrical power than the smaller unit. Different models of air conditioners may use electric power more or less efficiently. This prevents a direct conversion from BTUs to watts, but you can calculate the power used.
Read the appliance nameplate information and determine the number of amperes the appliance draws and the voltage on which it operates. Most modern appliances supply the information on a metal plate or sticker and in accompanying documentation.
Multiply the current in amperes by the voltage. The result is volt-amperes, which equals the number of watts used by the device.
Electric utility companies sell power in kilowatts. Multiply watts by 1,000 to convert to kilowatts.
Michael Logan is a writer, editor and web page designer. His professional background includes electrical, computer and test engineering, real estate investment, network engineering and management, programming and remodeling company owner. Logan has been writing professionally since he was first published in "Test & Measurement World" in 1989.