Calories to Kilojoules
Convert calories (cal) to kilojoules (kJ). Both measure work and power, and the conversion comes up in nutrition, electricity, fitness work.
The Formula
``
kilojoules = calories × 0.004184
calories = kilojoules × 239.005736138
`
One calory is 0.004184 kilojoules, and one kilojoule is 239.0057 calories.
Conversion Table
| 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 |
| 500 cal | 2.092 kJ |
| 1,000 cal | 4.184 kJ |
The Other Direction
| Kilojoules | Calories |
|---|---|
| 1 kJ | 239.0057 cal |
| 2 kJ | 478.0115 cal |
| 5 kJ | 1,195.03 cal |
| 10 kJ | 2,390.06 cal |
| 25 kJ | 5,975.14 cal |
| 50 kJ | 11,950.29 cal |
| 100 kJ | 23,900.57 cal |
| 500 kJ | 119,502.87 cal |
| 1,000 kJ | 239,005.74 cal |
What Each Unit Is
Calories (cal) — the energy to raise one gram of water by one degree Celsius, or 4.184 joules — the "small" calorie. A 19th-century thermal unit, displaced by the joule in physics but retained in nutrition.
Kilojoules (kJ) — 1,000 joules. The metric food-energy unit outside North America.
A Sense of Scale
A gram of sugar holds about 4,000 small calories- An apple holds about 400 kJ
- Daily intake is around 8,700 kJ
Precision
The factor 0.004184 is rounded. For engineering work carry more digits than the table above, and round only at the end — rounding at each step compounds.
Watch Out For
- Food labels say "calorie" but mean kilocalorie — 1,000 of these. A 200-calorie snack is 200 kcal, or 837 kJ.
In Code
`javascript
const calorieToKilojoule = (value) => value * 0.004184;
``
Where This Conversion Comes Up
- Nutrition
- Electricity
- Fitness
- Heating
- Fuel
How Many Decimals Do You Need?
Rounding the factor costs accuracy, and how much depends on the factor. Converting 137 cal with the factor truncated at each decimal place:
| Decimals kept | Factor | 137 cal becomes | Error |
|---|---|---|---|
| 0 | 0 | 0 | 100.0000% |
| 1 | 0 | 0 | 100.0000% |
| 2 | 0 | 0 | 100.0000% |
| 3 | 0.004 | 0.548 | 4.3977% |
| 4 | 0.0042 | 0.5754 | 0.3824% |
The right number of significant figures is set by your input, not by the converter. If you measured calories to three significant figures, the answer in kilojoules is only good to three — writing more digits claims precision the measurement never had.