# Eli5:why is that something rated 1000w spends 1kWh after an hour instead of 3600kWh, since watt is by second?

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Eli5:why is that something rated 1000w spends 1kWh after an hour instead of 3600kWh, since watt is by second?

In: Other Because the kilowatt-hour is a unit used by electric companies to measure the power usage of something per hour. Just multiply the kilowatt times an hour (or 3600 seconds). Something rated 1000w will spend 1 kW every second, but it will take an hour to spend 1kWh. Because the unit kWh is kiloWatt hours. It has the second to hour conversion in it.

1 kWh = 3.6 megajoules Watts are a measure of the *rate* of energy transfer, while watt-hours are a *quantity* of energy.

Watts is “joules per second.” A watt-hour is one watt **for** one hour, equivalent to 3600 joules (one per second, for 3600 seconds.) One thousand watts (joules per second) — also known as a kilowatt — for one hour (3600 seconds) is 1000 watt-hours or one kilowatt-hour or or 3,600,000 joules or 3.6 megajoules. It will expend 1000 Wh = 1kWh but it will spend 3600 kWs = 3600 kilojoule (kJ) = 3.6 megajoules.

Joules and kWh are different scales of the same measurement. The first is useful to the guy designing the machine to not burn up. The other, to the guy billing people to use it.

It’s kind of like: Einstein says mass is equivalent to energy. If we wanted, we could measure the mass of that chocolate bar in (billions of billions of) the same unit as we measure it’s food energy in (calories). But we’d rather not.