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Energy
Kilojoules to Joules
Convert kilojoules (kJ) to joules (J). Type a value below to see the result update instantly. Reference table and formula included.
Calculator
1 kJ = 1000 J
Kilojoules to Joules Conversion Table
Common values, ready to copy:
| kilojoules | joules |
|---|---|
| 1 kJ | 1000 J |
| 2 kJ | 2000 J |
| 5 kJ | 5000 J |
| 10 kJ | 10000 J |
| 25 kJ | 25000 J |
| 50 kJ | 50000 J |
| 100 kJ | 100000 J |
| 1,000 kJ | 1.0000e+6 J |
Formula
joules = kilojoules × 1000
Energy uses the SI joule. Food calories (kcal) are 1,000 small calories: 1 kcal = 4,184 J. 1 kWh = 3.6 MJ = 3,600,000 J. 1 BTU = 1,055.06 J.
About Kilojoules and Joules
Kilojoules (kJ): A thousand joules; the practical SI energy unit for food and nutrition in metric countries. Common uses: Food energy labeling outside the US, electrical energy in kJ for small batteries, and biology (metabolism).
Joules (J): The SI unit of energy; named for James Prescott Joule, whose 19th-century experiments established the equivalence of mechanical work and heat. Common uses: Physics calculations, food calorie labeling in metric countries (kilojoules), battery capacity, and chemistry.
How the conversion works
Energy uses the SI joule. Food calories (kcal) are 1,000 small calories: 1 kcal = 4,184 J. 1 kWh = 3.6 MJ = 3,600,000 J. 1 BTU = 1,055.06 J.
The exact relationship is joules = kilojoules × 1000, which the calculator at the top of this page applies in both directions. Type into either field and the other updates immediately.
When this conversion matters
Converting between kilojoules and joules comes up wherever energy measurements move between systems — from one country's conventions to another's, from a scientific reference to a practical specification, or from one industry's working unit to another's. The calculator and reference table above cover the everyday range; for unusual values you can type any number into either field.