Construct a power requirements table. On a piece of paper, draw a table with four columns. Label the first column of the table, "Electronic Device"; the second column, "Power (Watts)"; the third column, "Hours"; and the fourth, "Watt-Hours." Add one row for each electronic device you use. In the Electronic Device column, write down the name of each electronic device you use on each of the rows. In the Hours column, write down the number of hours you use each electronic device per month.
Compile a list of the power requirements for each of your electronic devices. Look first in your electronic device's owners manuals. If you can't find the power specification there, call the manufacturer. Otherwise, look for the power specifications on the Internet. You can search using the manufacturer's name or the model and make of the electronic device. Also examine the electronic device power tables produced by such organizations as The United States Department of Energy (see Resources section) and utility companies. Look for tables that list power requirements for specific types of electronic devices. Some utility companies have power calculators on their websites with extensive electronic device lists.
For each power rating you obtain for your electronic device, write down the power in the Power column in the corresponding row for the electronic device. If the power rating is in milliwatts, divide by 1,000 to convert milliwatts to watts. Milliwatts are often expressed as "mw." Watts is also often abbreviated as "w."
Calculate your watt-hours needs. For each row in your table, multiply the number in the Watts column by the number in the Hours column. Place that result in the Watt-Hours column on the same row.
Add your total watt-hour needs. Add all the numbers in the Watt-Hours column. This number is your total power needed in watt-hours per month.
Calculate your kilowatt-hour needs. Divide the total power needed obtained in the previous step by 1,000. This is the power you need in kilowatt-hours per month. Power needs are often expressed in kilowatt-hours. "Kilo" means 1,000 and "kilowatt-hour" means 1,000 watt-hours.