The exact equivalent
A kilowatt hour is exactly 3,600,000 joules. It is 1,000 watts sustained for 3,600 seconds, and a watt is a joule per second.
1 kWh = 3,600,000 J
1 J = 0.00000028 kWh
How to convert it by hand
Just multiply by the conversion factor. To go from kilowatt hours to joules, multiply by 3,600,000; to come back, divide by that same number or multiply by 0.
For example: 25 kWh × 3,600,000 = 90,000,000 J.
A tip that saves mistakes: check the result goes the way you expect. If joules are a smaller unit than kilowatt hours, the number has to come out bigger. If it comes out smaller, you divided when you should have multiplied.
Conversion table
| kWh | J |
|---|---|
| 1 | 3,600,000 |
| 2 | 7,200,000 |
| 5 | 18,000,000 |
| 10 | 36,000,000 |
| 20 | 72,000,000 |
| 50 | 180,000,000 |
| 100 | 360,000,000 |
Reference points to picture it
| Reference | Equals |
|---|---|
| 1 kWh | 3.6 MJ |
| A day of household use | 10 kWh = 36 MJ |
| An electric car battery | 60 kWh = 216 MJ |
| A 60 W bulb for an hour | 0.06 kWh = 216 kJ |
The trick for doing it in your head
Multiply by 3.6 million. For 2 kWh: 7.2 million joules, or 7.2 megajoules.
It is fine for getting by without a phone, but not for anything that depends on precision: in a recipe, on a building site or in a dose, use the exact conversion.