Find the wattage of the electrical items you are measuring. If the wattage is not printed on the unit, check the manual to see what the wattage is.
Figure out, measure or estimate the number of hours each unit will run for the time period you are measuring.
Multiply the wattage by the number of hours used to get a figure for watt-hours for each unit. As an example, if you have an appliance that runs at 200 watts, and you use it for 4 hours, that is 800 watt-hours.
Add the total of watt-hours for all the units you are measuring.
Divide the watt-hours total by 1,000 to get a figure for kWh. If your watt-hour total is 15,000, for instance, your kWh total is 15.