Joules to Kilojoules
Convert joules to kilojoules instantly. 1 J = 0.001 kJ. Includes the exact factor, a conversion table of common values and the definition of both units.
How to convert joules to kilojoules
To convert joules to kilojoules, divide by 1,000 (multiply by 0.001). The relationship is fixed, so the same factor works for any quantity — there is nothing to look up and nothing that changes with temperature, location or context.
kJ = J × 0.001
Joules to Kilojoules conversion table
The values people look up most often, rounded for reading. Use the calculator above for anything in between.
| Joules | Kilojoules |
|---|---|
| 1 J | 0.001 kJ |
| 2 J | 0.002 kJ |
| 3 J | 0.003 kJ |
| 5 J | 0.005 kJ |
| 10 J | 0.01 kJ |
| 20 J | 0.02 kJ |
| 25 J | 0.025 kJ |
| 50 J | 0.05 kJ |
| 100 J | 0.1 kJ |
| 500 J | 0.5 kJ |
| 1,000 J | 1 kJ |
What is a joule?
The SI unit of energy: one newton-metre, or one watt for one second.
What is a kilojoule?
A thousand joules. Food energy is labelled in kilojoules outside the US.
The formula
kJ = J × 0.001
Every result on this page comes from this formula. Nothing is rounded until the final display, so figures match a spreadsheet to the cent.
How to use the Joules to Kilojoules
- Type the number of joules you want to convert.
- Read the result in kilojoules straight away — there is no button to press.
- Check the table below for the values that come up most often, or reverse the conversion with the linked kilojoules to joules page.
Joules to Kilojoules — frequently asked questions
How many kilojoules are in a joule?
One joule equals 0.001 kJ. kJ = J × 0.001
What is the formula to convert joules to kilojoules?
The formula is kJ = J × 0.001. It is an exact definition rather than an approximation, so the conversion never drifts no matter how large the number.
How do I convert kilojoules back to joules?
Divide instead of multiplying: one kilojoule is 1,000 J. The reverse converter is linked in the related tools list.
Is this conversion exact?
Yes. Both units are defined against the same base unit by international agreement, so the factor is exact — any rounding you see is only in the display, which you can widen by entering more decimal places.
Is this joules to kilojoules free to use?
Yes. Every calculator on the site is free, needs no sign-up, and runs entirely in your browser, so your figures never leave your device.
What people search for
This page answers each of these searches. They are the exact phrases visitors use to find the joules to kilojoules.
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About this calculator
Written and reviewed by The Samsung Calculator editorial team. Every calculator is written against a published formula, reviewed against at least one independent reference implementation, and dated when it changes.
Last reviewed August 19, 2026 · Calculation runs client-side · No data collected · Report an error