SafekipediaKilowatt-hour
Adapted from Wikipedia · Adventurer experience
A kilowatt-hour (written as kW⋅h or kWh) is a way to measure energy. It tells us how much energy is used when one kilowatt of power works for one hour. We use this unit to know how much electricity we use at home or elsewhere.
Kilowatt-hours are important because companies that give us electricity use them to count how much energy people use. Your electricity bill will show how many kilowatt-hours you used.
One kilowatt-hour equals 3.6 megajoules of energy, which is another way to measure energy. This unit helps scientists and engineers talk about energy clearly and easily.
Definition
The kilowatt-hour is a way to measure energy. It tells us how much energy is used when something with a power of one kilowatt runs for one hour. In the International System of Units, energy is measured in joules. Since a watt is one joule per second and there are 3,600 seconds in an hour, one kilowatt-hour equals 3,600 kilojoules or 3.6 megajoules.
Unit representations
The most common way to write the kilowatt-hour is kWh. Companies that provide electricity, schools, and scientists use this. Even though it is widely used, it does not follow the exact rules set by the International System of Units (SI).
You might also see kW⋅h or kW h. These follow the SI rules better. Some places, like the United States, have used kW-hrs on car stickers for electric vehicles. Sometimes, people write it in different ways like KWh or KWH, but these are not the preferred ways. Writing kW/h is wrong because it means something different.
Electricity sales
Electricity is sold in kilowatt-hours. To find out how much it costs to run a device, multiply its power use in kilowatts by the number of hours it runs, and then by the price per kilowatt-hour. The price of electricity can change depending on where you live and how much you use.
Big customers might pay for the highest amount of power they use in a short time, like 15 minutes. This helps pay for special equipment needed for big bursts of power. Very large users might have extra charges based on how their power use changes.
Big amounts of energy are often talked about in terawatt-hours (TWh) for a whole year. One gigawatt running all year equals about 8.76 terawatt-hours of energy.
Examples
In 2020, the average household in the United States used about 893 kWh each month. This is like using power all the time at an average of 1.22 kW.
Heating 1 litre of water from room temperature to boiling with an electric kettle needs around 0.1 kWh. A 12-watt LED lamp that stays on all day uses about 0.3 kWh, or around 9 kWh each month.
Conversions
Further information: Conversion of units § Energy
To change a measurement from one unit to another, like turning hours into minutes, you multiply by a special number. This helps you see how much energy you are using or getting in different ways.
| Joule | Watt-hour | Kilowatt-hour | Electronvolt | Calorie | |
|---|---|---|---|---|---|
| 1 J = 1 kg⋅m2⋅s−2 = | 1 | 2.77778 × 10−4 | 2.77778 × 10−7 | 6.241 × 1018 | 0.239 |
| 1 Wh = | 3.6 × 103 | 1 | 0.001 | 2.247 × 1022 | 859.8 |
| 1 kWh = | 3.6 × 106 | 1,000 | 1 | 2.247 × 1025 | 8.598 × 105 |
| 1 eV = | 1.602 × 10−19 | 4.45 × 10−23 | 4.45 × 10−26 | 1 | 3.827 × 10−20 |
| 1 cal = | 4.184 | 1.162 × 10−3 | 1.162 × 10−6 | 2.612 × 1019 | 1 |
Watt-hour multiples
Further information: Metric prefix
SI prefixes are used with the watt-hour. For example, a kilowatt-hour (kWh) is 1,000 watt-hours, and a megawatt-hour (MWh) is 1 million watt-hours. These bigger units help us measure the energy used by large factories and the electricity made by power plants. The kilowatt-hour is the unit most often used by electricity companies to bill homes for their monthly energy use. Even larger units like gigawatt-hours (GWh) and terawatt-hours (TWh) are used to talk about all the electricity made by countries or the whole world in a year.
| Value | Symbol | Name |
|---|---|---|
| 10−6 | μW⋅h | microwatt-hour |
| 10−3 | mW⋅h | milliwatt-hour |
| 100 | W⋅h | watt-hour |
| 103 | kW⋅h | kilowatt-hour |
| 106 | MW⋅h | megawatt-hour |
| 109 | GW⋅h | gigawatt-hour |
| 1012 | TW⋅h | terawatt-hour |
| 1015 | PW⋅h | petawatt-hour |
Distinction between kWh (energy) and kW (power)
A kilowatt measures how much power we use at any moment. A kilowatt-hour tells us how much energy we used over an hour. For example, if you have a light that uses 1 kilowatt and leave it on for 1 hour, you used 1 kilowatt-hour of energy.
A battery holds energy. When we use that energy, we do it at a certain power level. The higher the power, the faster the battery’s energy runs out.
Other related energy units
Main article: Units of energy
There are other ways to talk about energy that are related to the kilowatt-hour. For example, we can measure how much energy something uses or makes in a whole year using kilowatt-hours per year. This helps us compare things like how much energy home appliances use over time.
Batteries often show their power in ampere-hours. To find out how much energy they store, we multiply this number by the battery's voltage. But keep in mind, this is just an estimate because the battery's voltage changes as it loses power.
Related articles
This article is a child-friendly adaptation of the Wikipedia article on Kilowatt-hour, available under CC BY-SA 4.0.
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