Determine the average wattage rating for each electronic device or appliance. You can look up the average or typical watt ratings for individual appliances and electronic devices on tables produced by the Energy Department. Alternately, you can use a number of other tables offered by your local electricity providers and appliance companies. For computers, there are special PC power calculators that accurately estimate the watt rating for different types of PCs and PC configurations.
Record the number of hours your electronic device is used each day for several days in a row. Fourteen days is sufficient because it includes two weekends and ten workdays, thus giving you a more accurate record.
Total the number of hours you used the electronic device each day. If your used your device for 14 days in a row, you will have 14 numbers to add. If you used your device for 30 days in a row, you will have 30 numbers to add.
Multiply the total number of hours you used the electronic device by its watt rating. The resulting number represents the watt-hours your device was used over the time period.
Divide the watt-hours by the number of days you used the device. This number is the average watts used per day.