Determine the direct current that your electronic device consumes. Contact the manufacturer, look on the electronic devices data sheet or measure the current with ammeter, a device that measures current.
Convert the current value in the units given to amperes. If the current is given in milliamperes, divide the current by a 1,000 to convert milliamperes to amperes. If the current is given in microamperes, multiply the current by 1 million to convert microamperes to amperes.
Determine the voltage that the electronic device operates at. Contact the manufacturer, measure the voltage with a voltmeter, note the voltage rating on the device's label or read the data sheet to find out the operating voltage of the device.
Multiply the operating voltage of the electronic device in volts by the current rating in amperes to obtain the power consumption of the device in watts. For example, if the voltage rating of the device was 12 volts and the current rating was 0.01 amperes, the power consumption would be 0.12 watts
Multiply the power consumption in watts by the time in hours that the electronic device will be operated to compute the kilowatt hours to convert the DC to KWH. For example, if the the power consumption was 0.12 watts and the time the device was operated was 2 hours, the kilowatt hours would be 0.24 kilowatt hours since 2 times 0.12 is 0.24.