# What is the difference between KW and KWh?

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Update: I am actually searching for really simple, intuitive ways to explain it. I have a background in engineering, but am struggling to explain why we “pay for kwh”, and not kw (on our electricity bill) to someone who doesn’t. I have tried in many ways but maybe I’m not giving the right examples or making the right comparisons. I am really searchig for a way to ELI5.

In: 24  One is a rate of power expenditure, and one is a quantity of energy spent (or stored.. batteries also have a Wh value associated with them, or more commonly mAh which can be converted to Wh using the voltage of the battery (milliAmp hours)). Power (Standard unit of Watts) is defined as energy per time (Joules/Second)

kW is the *rate* of power consumed when you use a device.

If a device requires 1 kW and you use it for 1 hour, you have used a *quantity* of 1 kWh.

This is how energy companies measure your power usage, by how many kWh you use per month. Different amounts put you in different tiers, which give you different rates.

Edit: added the words “spent (or stored)” for clarity, changed a few things for accuracy When you start pushing a cart, you keep applying an amount of power to it, measured in KW, so that it keeps moving.

All the cart pushing while you do your shopping is measured in KWh: KW per hour, e.g. the total amount of energy used by you during that shopping cycle. Think of it as gas mileage on your car. The trip computer will tell you at any one time how much fuel you’re currently using but to know how much you’ve used in total you need to multiply that by the distance you’ve travelled.

A kW rating tells you how much energy a device uses at any one moment, but to know how much energy you’ve used in total you need to multiply that by how long you’ve used it for. The standard unit of energy is the Joule. Joules could be used to describe the energy stored in a battery, in a gallon of gasoline, in food (Calories are also a unit of energy), and so on. Energy being transferred over time is such a commonly used concept, that we gave the unit its own name: the Watt. 1 Watt = 1 Joule per second.

1 Watt is actually a small amount, so often we use kilowatts (kW) instead. 1 kW = 1000 W = 1000 J/s.

A kilowatt-hour is the amount of energy needed to transfer energy at 1000 Watts for an hour. There are 3600 seconds/hour, so 1 kWh =1 kJ/s * 1 hour = 1 kJ/s * 3600 seconds = 3600 kJ = 3.6 MJ.

We often use kWh instead of megajoules because we want to answer questions like “how many hours will my battery last?” and not “how many seconds will my battery last?”. They’re technically equivalent, but kWh is more convenient.