Kilojoules to Joules
An instant kilojoules-to-joules converter, with the formula and a reference table below.
| Kilojoules | Joules |
|---|---|
| 1 kJ | 1000 J |
| 2 kJ | 2000 J |
| 3 kJ | 3000 J |
| 5 kJ | 5000 J |
| 10 kJ | 10000 J |
| 25 kJ | 25000 J |
| 50 kJ | 50000 J |
| 100 kJ | 100000 J |
How to use
- Enter a value in the Kilojoules field.
- The Joules figure appears immediately — no button to press.
- Typing in the Joules field converts back to Kilojoules the same way.
- Use the reference table for the values that come up most often.
Kilojoules to Joules formula
The factor from kilojoules to joules is 1000.
J = kJ × 1000
Put another way, one kilojoule is exactly 1,000 joules.
Why this factor: the kilojoule and the joule are both defined against the joule, so dividing one definition by the other gives 1000 directly. Both definitions are set out in full below.
To go the other way, divide by 1000 — or use the Joules to Kilojoules converter, which is the same calculation reversed.
Worked example
Start with 100 kJ. Multiply by 1000 to get 100000 J.
100 kJ × 1000 = 100000 J
The converter above does this for any value you type, in either direction.
What is a kilojoule?
A kilojoule is 1,000 joules, the metric unit of food energy.
Definition: Exactly 1,000 joules.
Where it is used: Nutrition labels in Europe and Australia, and heating and cooling loads.
What is a joule?
The joule is the SI unit of energy — the work done by one newton acting over one meter.
Definition: Defined as 1 N·m, equivalently one watt-second. Named after James Prescott Joule.
Where it is used: All scientific energy calculations, food energy on European labels, and mechanical work.
Kilojoules vs Joules
The kilojoule is a metric unit while the joule is an SI unit. That is why the factor between them is not a round number: the two systems were defined independently and only later tied together by exact agreement.
Frequently asked questions
How many joules are in a kilojoule?
One kilojoule equals 1000 joules.
What is the formula to convert kilojoules to joules?
Multiply the number of kilojoules by 1000. To reverse it, divide by 1000 instead.
How do I convert joules back to kilojoules?
Divide by 1000, which is the same as multiplying by 0.001.
How many joules are in 10 kilojoules?
10 kJ works out to 10000 J.
How is the kilojoule defined?
Exactly 1,000 joules.