How joules and kilojoules are converted
1,000 J = 1 kJ. In reverse, 2.5 kJ = 2,500 J.
kilojoules = joules ÷ 1,000; joules = kilojoules × 1,000
- Divide joules by 1,000 to find kilojoules.
- Reverse the calculation to convert kilojoules back to joules.
- Only the displayed values are rounded. The conversion uses the full unit factor.
Worked example — 1,000 J = 1 kJ. In reverse, 2.5 kJ = 2,500 J.
Common joules to kilojoules values
| Joules | Kilojoules (kJ) |
|---|---|
| 1 J | 0.001 kJ |
| 10 J | 0.01 kJ |
| 100 J | 0.1 kJ |
| 1,000 J | 1 kJ |
| 5,000 J | 5 kJ |
| 10,000 J | 10 kJ |
Swipe the table sideways to see the rest.
Results use the same exact factors as the calculator.
Things to consider
- Check whether a food label uses kcal or kJ before comparing values.
- One dietary Calorie is one kilocalorie, equal to 4.184 kJ.
- Power in kilowatts needs a duration in hours to calculate energy in kWh.
- Negative amounts can represent an energy change, such as heat leaving a system.
Frequently asked questions
How do I convert joules to kilojoules?
Divide by 1,000. 1,000 J = 1 kJ. In reverse, 2.5 kJ = 2,500 J.
Can I convert kilojoules back to joules?
Yes. Choose the reverse direction. Multiply by 1,000.
Are food Calories the same as small calories?
No. A food Calorie means one kilocalorie (kcal), equal to 1,000 small calories (cal). This converter uses thermochemical calories: 1 kcal = 4.184 kJ.
Is a kilowatt-hour the same as a kilowatt?
No. Kilowatts measure power. Kilowatt-hours measure energy. At constant power, 1 kW for 1 hour uses 1 kWh.
Results are estimates for general information only, not financial, medical or professional advice.