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Convert joules to kilojoules
Instant, accurate J → kJ conversion with a live converter, table and formula.
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1 joule = 0.001 kilojoules
1 kilojoule = 1000 joules
joules to kilojoules table
| joules (J) | kilojoules (kJ) |
|---|---|
| 0.5 | 0.0005 |
| 1 | 0.001 |
| 2 | 0.002 |
| 5 | 0.005 |
| 10 | 0.01 |
| 20 | 0.02 |
| 50 | 0.05 |
| 100 | 0.1 |
| 500 | 0.5 |
| 1000 | 1 |
Formula
kilojoules = joules × 0.001.
Example
10 joules = 0.01 kilojoules.
What is a joule?
The joule (J) is the SI unit of energy.
What is a kilojoule?
A kilojoule (kJ) is 1,000 joules; food energy is often labeled in kJ.
Real-world reference points
A food Calorie is a kilocalorie: an apple is ~52 kcal, a daily diet ~2,000 kcal (~8.4 MJ).
| Reference | joules | kilojoules |
|---|---|---|
| AA battery | 15,390 J | 15.39 kJ |
| Smartphone battery (13 Wh) | 46,800 J | 46.8 kJ |
| Apple (52 kcal) | 218,000 J | 218 kJ |
| Daily diet (2,000 kcal) | 8,370,000 J | 8,368 kJ |
| 1 kWh (unit of electricity) | 3,600,000 J | 3,600 kJ |
Mistakes to avoid with energy conversions
- Food 'Calories' are kilocalories — mixing cal and kcal creates 1000× errors.
- Confusing kWh (energy) with kW (power) on bills and appliance labels.
- Comparing battery mAh across different voltages — energy needs Wh, not mAh alone.
Frequently asked questions
How many kilojoules in a joules?+
1 joule = 0.001 kilojoules.
How do I convert joules to kilojoules?+
Enter the value in the joules box above and the kilojoules value appears instantly. You can also type in the kilojoules box to convert the other way.
Is this J to kJ converter free?+
Yes — it is 100% free, needs no sign-up, and runs entirely in your browser.