Watts and kilowatts measure power
A watt measures the rate at which energy is transferred or used. One kilowatt equals exactly 1,000 watts.
To convert watts to kilowatts, divide by 1,000. A 1,500-watt heater has a power rating of 1.5 kW.
Kilowatt-hours measure energy
A kilowatt-hour measures energy, not power. Using 1 kilowatt continuously for 1 hour consumes 1 kilowatt-hour.
Energy in kWh equals power in kW multiplied by time in hours. A 1.5 kW heater running for 2 hours uses 3 kWh.
Estimate appliance operating cost
Multiply energy use in kWh by the electricity price per kWh. If 3 kWh costs $0.20 per kWh, the estimated energy charge is $0.60.
Actual cost can include fixed charges, time-of-use pricing, taxes, demand charges, and appliance cycling. Use the applicable rate structure.
Common power and energy mistakes
Do not write kW when the quantity is kWh. A device's kW rating describes how quickly it uses energy; kWh depends on operating time.
Use measured power when possible because devices may not draw their nameplate rating continuously. Standby modes and controls affect consumption.