A 5000 btu window unit can range from 500 to 650 watts based upon how much amperage the motor draws. To find the most accurate draw for your particular unit locate the manufactures specification tag, usually located on either side of the unit, then locate the stated amperage. Probably somewhere in the range of 4 to 6 amps, unless it's a power hog. Multiply that amperage times 120 and you should have the speculative wattage draw. (Amps X Volts = watts.) The only way to get an exact reading is to put a meter on it.