Joules to Calories
Convert joules (J) to calories (cal). Both measure work and power, and the conversion comes up in nutrition, electricity, fitness work.
The Formula
``
calories = joules × 0.239005736138
joules = calories × 4.184
`
One joule is 0.239006 calories, and one calory is 4.184 joules.
Conversion Table
| Joules | Calories |
|---|---|
| 1 J | 0.239006 cal |
| 2 J | 0.478011 cal |
| 5 J | 1.195 cal |
| 10 J | 2.3901 cal |
| 25 J | 5.9751 cal |
| 50 J | 11.9503 cal |
| 100 J | 23.9006 cal |
| 500 J | 119.5029 cal |
| 1,000 J | 239.0057 cal |
The Other Direction
| Calories | Joules |
|---|---|
| 1 cal | 4.184 J |
| 2 cal | 8.368 J |
| 5 cal | 20.92 J |
| 10 cal | 41.84 J |
| 25 cal | 104.6 J |
| 50 cal | 209.2 J |
| 100 cal | 418.4 J |
| 500 cal | 2,092 J |
| 1,000 cal | 4,184 J |
What Each Unit Is
Joules (J) — the work done by one newton acting over one metre — the SI derived unit of energy. Named for James Prescott Joule, who established the mechanical equivalent of heat.
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.
A Sense of Scale
Lifting an apple one metre takes about 1 J- A heartbeat uses roughly 1 J
- A gram of sugar holds about 4,000 small calories
Precision
The factor 0.239005736138 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 jouleToCalorie = (value) => value * 0.239005736138;
``
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 J with the factor truncated at each decimal place:
| Decimals kept | Factor | 137 J becomes | Error |
|---|---|---|---|
| 0 | 0 | 0 | 100.0000% |
| 1 | 0.2 | 27.4 | 16.3200% |
| 2 | 0.24 | 32.88 | 0.4160% |
| 3 | 0.239 | 32.743 | 0.0024% |
| 4 | 0.239 | 32.743 | 0.0024% |
The right number of significant figures is set by your input, not by the converter. If you measured joules to three significant figures, the answer in calories is only good to three — writing more digits claims precision the measurement never had.