The Watt (symbol: W) measures a rate of energy conversion. A human climbing a flight of stairs is doing work at a rate of about 200 watts. A typical automobile engine produces mechanical energy at a rate of 25,000 watts (approximately 33.5 horsepower) while cruising. A typical household incandescent light bulb uses electrical energy at a rate of 25 to 100 watts, while compact fluorescent lights typically consume 5 to 30 watts. Kilowatt The kilowatt (symbol: kW) is equal to one thousand watts. An electric heater with one heating element might use 1 kilowatt. Kilowatt hour The kilowatt hour is a convenient unit for electrical bills because the energy usage of a typical electrical customer in one month is several hundred kilowatt hours. kWh is the product of power in kilowatts multiplied by time in hours Confusion of watts and watt-hours Power and energy are frequently confused in the general media.
Power is the rate at which energy is used (or generated). For example, if a 100 watt light bulb is turned on for one hour, the energy used is 100 watt-hours or 0.1 kilowatt-hour. This same quantity of energy would light a 40-watt bulb for 2.5 hours. A power station would be rated in watts, but its annual energy sales would be in watt-hours (or kilowatt-hours or megawatt-hours). A kilowatt-hour is the amount of energy equivalent to a steady power of 1 kilowatt running for 1 hour.