Kilowatt vs. kilowatt-hour

The terms “kilowatt” and kilowatt-hour are commonly confused, but the terms refer to completely different things.

1,000 watts is a kilowatt. Likewise, 1,000 kilowatts is a megawatt; 1,000 megawatts, a gigawatt; and 1,000 gigawatts, a terawatt.

A hair dryer that has “1,000 watts” written on its label consumes a kilowatt of electricity when it is on full blast. If it runs for an hour, it has consumed a kilowatt-hour. An appliance that consumes 2,000 watts when it is on will consume 1,000 watt-hours (or a kilowatt-hour) when it runs for 30 minutes.

If you need a memory aid, think of kilowatts as horsepower – the amount of power your car’s engine can provide. Horsepower is then equivalent to kilowatts – the engine/appliance’s potential. But your car rarely runs at full horsepower, and most of the day it stands around doing nothing. So think of kilowatt-hours – the work done, as opposed to the potential – as, roughly, the number of kilometers driven.