Determine the power requirements of your electronic devices. Contact the manufacturer of the device and ask for a data sheet or find it on the Internet. Look on the data sheet, often called a specification sheet or spec sheet, for the electronic device's current rating and the voltage rating. This example will use a washing machine from General Electric.
Multiply the electronic device's current rating by its voltage rating. For the washing machine, the voltage is rated at 120 Volts and the current is rated at 12.0 amps. So the power rating is 1440 watts, since 120 times 12 is 1440.
Determine how long your device is on every year. For this washing machine example, first determine how many loads of laundry you wash every week. Then determine how long the washing machine is on for each load. Multiply the time per load (in hours) by the number of loads by the number of weeks in a year. There are 52 weeks in a year. If each load took 0.5 hours and you washed four loads per week, your washing machine would be on for 104 hours per year, since 0.5 times 4 times 52 is 104.
Calculate the watt-hours per year for your electronic device. Multiply the electronic device's power rating by the number of hours used over the year. From the examples above, the power is 1440 Watts and the number of hours per year the washing machine is on is 104 hours. So the number of watt-hours per year is 149,760 watt-hours since 1440 times 104 is 149,760.
Calculate the kilowatt-hours per year, that is the kw use per year, and then compare with the manufacturer's expected yearly usage. Divide watt-hours by 1000 to obtain kilowatt-hours. For this example, the number of kilowatt-hours would be 149.7 kilowatt-hours since 149,700 divided by 1000 is 149.7. General Electric states that its customers can expect to use 142 kilowatt-hours per year using that specific device.