Joules to kJ Converter
Convert joule to kilojoule instantly. 1 J = 0.001 kJ, worked steps and a full reference table.
How to use it
- Type the value in joule — the result updates as you type.
- Use Swap to flip the direction, or change either dropdown to convert between any two units.
- Click the result to copy it. The URL updates too, so you can bookmark or share the exact conversion.
Examples
| 1 J | 0.001 kJ |
| 5 J | 0.005 kJ |
| 10 J | 0.01 kJ |
| 100 J | 0.1 kJ |
One joule equals 0.001 kilojoules (kJ). To convert joules to kilojoules, multiply by 0.001; to go back the other way, multiply by 1000 instead.
The converter above does it as you type and shows the working underneath, so you can check the arithmetic rather than take the number on trust.
What joules and kilojoules actually measure
Joule (J) — The joule is the SI unit of energy — one watt for one second. Physics, mechanical work and food energy in most of the world.
Kilojoule (kJ) — A kilojoule is a thousand joules. Nutrition labels outside the US, and heating calculations.
Joules to kJ conversion table
The most common values, worked out in advance. Anything not listed can be typed straight into the converter.
| J | kJ |
|---|---|
| 1 J | 0.001 kJ |
| 2 J | 0.002 kJ |
| 5 J | 0.005 kJ |
| 10 J | 0.01 kJ |
| 25 J | 0.025 kJ |
| 50 J | 0.05 kJ |
| 100 J | 0.1 kJ |
How to convert joules to kilojoules by hand
Multiply the number of joules by 0.001.
For example, 25 J × 0.001 = 0.025 kJ.
Going the other way, divide by 0.001 — or multiply by 1000, which is the same thing and easier to do in your head.
Everything runs in your browser
There is no server involved in the calculation. The numbers you type never leave your device, nothing is logged, and the page keeps working with no connection once it has loaded. That is not a marketing line — it is simply how the tool is built, because a calculation like this has no reason to touch a network.
Questions people ask
How many kJ are in 1 J?
1 J equals exactly 0.001 kJ. Multiply any value in joule by 0.001 to get kilojoule.
Is anything uploaded to a server?
No. The whole calculation happens in your browser. Nothing is sent anywhere, and the page keeps working offline once loaded.
Last updated 18 August 2026