How single-use electricity cost is calculated
Convert device power to kilowatts and duration to hours. Energy per device equals kilowatts multiplied by hours and the active duty-cycle fraction. Multiply by the number of identical devices for total kilowatt-hours, then multiply by the entered price per kWh for cost.
Power and energy are different
Watts and kilowatts describe the rate of electricity use. Kilowatt-hours describe energy used over time. One kilowatt used continuously for one hour equals one kilowatt-hour, so power, duration, and tariff should not be entered as interchangeable values.
Use measured or nameplate power carefully
A nameplate rating may be a maximum rather than typical draw. Thermostats, compressors, heaters, chargers, and variable-speed devices can cycle or change power during a session. Use a meter or a representative duty cycle for a better estimate, and remember that utility bills may also include taxes, fixed charges, demand charges, or tiered rates.