Convert Kilojoules to Joules
Kilojoules to joules is the conversion you need when an energy figure is given in the larger unit but you need the plain, base one — for a physics problem, a spec sheet, or a nutrition figure. One kilojoule is exactly 1000 joules, so the number always gets a thousand times bigger when you switch from kilojoules to joules.
Kilojoules to Joules conversion table
| Kilojoules (kJ) | Joules (J) |
|---|---|
| 1 | 1,000 |
| 2 | 2,000 |
| 3 | 3,000 |
| 5 | 5,000 |
| 10 | 10,000 |
| 20 | 20,000 |
| 50 | 50,000 |
| 100 | 100,000 |
| 500 | 500,000 |
| 1,000 | 1,000,000 |
The formula
To convert kilojoules to joules, multiply the number of kilojoules by 1000:
joules = kilojoules × 1000
A worked example
Say you have 250 kJ and want it in joules:
250 × 1000 = 250,000 J
So 250 kilojoules is exactly 250,000 joules.
Why the number is exact
The "kilo" prefix in the metric system means exactly one thousand — the same thousand you get in a kilometer or a kilogram. So one kilojoule is exactly 1000 joules by definition, with nothing rounded away. That makes this one of the cleanest conversions there is: just add three zeros.
When you'll use it
Working through physics or chemistry problems that want energy in base joules, reading spec sheets that mix the two units, or lining up a kilojoule figure against a value already given in joules.
Frequently asked questions
How many joules are in a kilojoule?
Exactly 1000 joules. The 'kilo' prefix means a thousand, so a kilojoule is a thousand joules — nothing rounded.
Is the kilojoules to joules conversion exact?
Yes. 'Kilo' means exactly 1000, so 1 kilojoule is exactly 1000 joules. It's an exact definition, not a rounded factor.
How do I turn joules back into kilojoules?
Divide by 1000. Since a kilojoule is exactly 1000 joules, going the other way just moves the decimal three places.