# What is a “kilowatt hour”?

A kilowatt hour, or one thousand watt hours, is a way of measuring the amount of electricity used or generated over time.

A standard old style light blub uses 100 watts of power to create light. If you leave one of those lights on for 10 hours, it will use 1,000 watt hours of electricity, or 1 kilowatt hour.

Think of it like your car:

60 km/h for 2 hours = 120 km (km/h x h = km) 60 watts for 2 hours = 120 watt hours (W x h = Wh)

Some devices use a constant amount of electricity. Light bulbs use a certain amount to make light and it doesn’t go up or down. But other devices use a variable amount of electricity. Your fridge does not always have its compressor running, and your computer does not always have its hard drives spinning.

So the amount of power you use is in constant flux, not just because you turn things on and off, but because each thing may be using different amounts of power from moment to moment.

Kind of like how you can spend two hours driving 120 kilometers, but your speed is certainly not steady at 60 km/h for the entire time.