The first step to using a kilowatt-per-hour calculator is to know which appliances are used and how often you use them, Piedmont Membership Energy Corporation explains. You also must know the rate charged by the local utility company to calculate energy costs.
Some power-company websites provide kilowatt-per-hour and cost calculators that allow users to estimate their energy usage and costs, Piedmont Membership Energy Corporation explains. These calculators automatically add the kilowatt-per-hour rate into the calculation. Simply enter the type and number of each appliance you use and how many hours a day you use them, and click Calculate. Other calculators require that you enter the energy rate manually in order to determine energy costs; the rate typically is included on the energy bill, says Electricity-Usage.com. You may need to do multiple calculations if the power company bills on a tiered system in which costs increase with the amount of energy used, as Pacific Gas and Electric Company explains.
It is also possible to calculate kilowatts-per-hour manually by multiplying the power usage in watts by the number of hours of usage and dividing by 1,000, Rapid Tables explains. For example, if you use a 3,000 watt oven for two hours, the total kilowatt-hours of energy consumed by the appliance is 6,000 divided by 1,000, or 6. To determine the cost of using the appliance, multiply the kilowatts-per-hour times the energy rate.