kilojoule (kJ)
1 kilojoule = 1,000 joules
What is kilojoule?
A kilojoule is a unit of energy equal to 1,000 joules. It is commonly used in nutrition to express the energy content of food, as well as in thermodynamics and mechanical engineering.
Notes: Metric unit
Real-world uses
Kilojoules are the standard energy unit for food nutrition labelling in Australia, New Zealand, and parts of Europe (alongside kilocalories). A typical adult daily intake is about 8,700 kJ. They are also used in chemistry for reaction enthalpies and combustion energies.
History
The kilojoule became important in nutrition labelling as countries adopted SI-based energy reporting. Australia was among the first to mandate kJ on food labels in the 1970s. The EU requires both kJ and kcal on nutrition labels.
Common mistakes
Confusing kilojoules with kilocalories—1 kcal = 4.184 kJ. Food labels showing "2000 kJ" are about 478 kcal, not 2000 kcal. Also, some people incorrectly assume kJ and kW are the same thing; one is energy, the other is power.
When is this conversion used?
Electricity bills use kilowatt-hours while physics calculations use joules. Converting between them is essential for energy audits, comparing appliance efficiency, and understanding power consumption. Nutritional information is labelled in kilocalories in some countries and kilojoules in others, making this conversion important for dietary planning and food science.
How to convert kilojoule to joule
To convert kilojoule to joule, multiply the value by 1,000.
Conversion formula (from base unit)
x * 1000.0
Measurement standards
The joule is the SI derived unit of energy, defined as one kilogram-metre-squared per second-squared (kg·m²/s²). The kilowatt-hour, equal to exactly 3.6 megajoules, is accepted for use with the SI by the BIPM for practical electricity metering.
Did you know?
A single bolt of lightning releases roughly 1 to 5 gigajoules of energy, yet only a small fraction reaches the ground as electrical current. Most of the energy dissipates as light, heat, and the thunder shockwave.
| kilojoules | joules |
|---|---|
| 0.1 | 100 |
| 0.5 | 500 |
| 1 | 1,000 |
| 2 | 2,000 |
| 5 | 5,000 |
| 10 | 10,000 |
| 25 | 25,000 |
| 50 | 50,000 |
| 100 | 100,000 |
| 250 | 250,000 |
| 500 | 500,000 |
| 1,000 | 1,000,000 |
Common values
| kilojoules | joules | |
|---|---|---|
| A food calorie (1 kcal) | 4.184 kilojoules | 4,184 joules |
| A AA battery | 9.36 kilojoules | 9,360 joules |
| Boiling a kettle | 420 kilojoules | 420,000 joules |
| Daily human diet (2000 kcal) | 8,368 kilojoules | 8,368,000 joules |
| 1 gallon of gasoline | 131,760 kilojoules | 131,760,000 joules |
Full kilojoule conversion table
| Unit | Value | Factor |
|---|---|---|
| joule | 1 kJ = 1,000 J | × 1,000 |
| kilowatt hour | 1 kJ = 0.00027778 kWh | × 0.00027778 |
| calorie (thermochemical) | 1 kJ = 239.00573614 cal | × 239.00573614 |
| kilocalorie (dietary) | 1 kJ = 0.23900574 kcal | × 0.23900574 |
| watt hour | 1 kJ = 0.27777778 Wh | × 0.27777778 |
| megajoule | 1 kJ = 0.001 MJ | × 0.001 |
| electronvolt | 1 kJ = 6.241509e+21 eV | × 6.241509e+21 |
| British thermal unit | 1 kJ = 0.94781712 BTU | × 0.94781712 |
| therm (US) | 1 kJ = 0.00000948 therm | × 0.00000948 |