Joules (J) to Kilojoules (kJ) Conversion
Joules
The joule (J) is the SI derived unit of energy, work, and heat, defined as the work done when a force of one newton displaces an object by one metre (J = N·m = kg·m²·s⁻²). Named after James Prescott Joule, who established the mechanical equivalent of heat in the 1840s, the joule unifies all forms of energy — mechanical, thermal, electrical, chemical, and nuclear — under one framework. One joule is small: lifting an apple (≈100 g) one metre requires about 1 joule, while a human at rest metabolises approximately 80 joules per second.
Kilojoules
The kilojoule (kJ) is a unit of energy equal to exactly 1,000 joules. It is the standard unit for expressing food energy in most countries outside the United States, where food labels display energy in both kilojoules and kilocalories (kcal). One kilocalorie equals exactly 4.184 kilojoules. In thermodynamics and chemistry, reaction enthalpies and bond energies are commonly tabulated in kilojoules per mole (kJ/mol).
| Joules (J) | Kilojoules (kJ) |
|---|---|
| 0.1 J | 0.0001 kJ |
| 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 |
| 30 J | 0.03 kJ |
| 50 J | 0.05 kJ |
| 100 J | 0.1 kJ |
| 1000 J | 1 kJ |
Frequently Asked Questions (FAQ)
How many kilojoules are in 1 joules?
1 joules (J) is exactly 0.001 kilojoules (kJ).
How do I convert joules to kilojoules?
Multiply the value in joules by 0.001 to get the result in kilojoules. Or use the converter above — type any number and see the result instantly.