Bills are figured on your use of kilowatt hours, which are 1,000 watt hours. You can figure the cost per month for an appliance from its wattage. For example, let's say that all of the light bulbs in your house are 100 watts, and your family has had the lights on for a total of 200 hours last month. Multiply the 200 hours last month by the 100 watts and you have 20,000 watt hours, or 20 kilowatt hours. Multiply the 20 kilowatt hours times the cost per kilowatt hour. If each kilowatt costs 6 cents, the lights cost $1.20 for the month.
All electrical appliances have the wattage listed somewhere on the appliance. You can use this figure to determine the cost of operation.