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Energy
Calories to Kilojoules
Convert calories (cal) to kilojoules (kJ). Type a value below to see the result update instantly. Reference table and formula included.
Calculator
1 cal = 0.004184 kJ
Calories to Kilojoules Conversion Table
Common values, ready to copy:
| calories | kilojoules |
|---|---|
| 1 cal | 0.004184 kJ |
| 2 cal | 0.008368 kJ |
| 5 cal | 0.02092 kJ |
| 10 cal | 0.04184 kJ |
| 25 cal | 0.1046 kJ |
| 50 cal | 0.2092 kJ |
| 100 cal | 0.4184 kJ |
| 1,000 cal | 4.184 kJ |
Formula
kilojoules = calories × 0.004184
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 Calories and Kilojoules
Calories (cal): Originally defined as the energy to raise one gram of water by one degree Celsius; exactly 4.184 J in the modern definition (the thermochemical calorie). Common uses: Scientific work in chemistry, where the small calorie is the natural unit for heat-of-reaction measurements.
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).
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 kilojoules = calories × 0.004184, 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 calories and kilojoules 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.