The calories to joules formula
To convert calories to joules, multiply by 4.184: J = cal × 4.184. For example, 100 cal × 4.184 = 418.4 J. One thermochemical calorie equals exactly 4.184 joules. To reverse it, use the joules to calories calculator.
The joule is the SI unit of energy: one joule is the work done when a force of one newton moves an object one metre. The calorie predates it and was defined by heating water - roughly the energy needed to raise one gram of water by one degree Celsius. Because that depends on the starting temperature, the calorie was later fixed by definition at 4.184 J rather than measured.
How to convert cal to J
Enter an energy value in calories and the calculator multiplies by 4.184 to give joules, the SI unit of energy. If you are working with food Calories (kcal), multiply by 1000 first, since one food Calorie equals 1000 small calories.
Worked example: a snack bar labelled 250 Calories contains 250 kcal. Convert to small calories first (250 x 1000 = 250,000 cal), then multiply by 4.184 to get 1,046,000 J, or 1046 kJ. This is exactly why European labels print kJ next to kcal. Mixing the two is the single most common mistake here - a value that looks 1000 times too large or too small almost always means kcal and cal were swapped.
People working on this usually reach for the kilowatts to horsepower calculator too.
Calories to joules reference table
| Calories | Joules |
|---|---|
| 1 cal | 4.184 J |
| 100 cal | 418.4 J |
| 500 cal | 2092 J |
| 1000 cal | 4184 J |
Useful reference points: 1 kJ = 1000 J, 1 kcal = 4184 J, and one watt-hour is 3600 J, so 1 kcal releases a little more energy than one watt-hour. Keep the same unit on both sides of any energy balance before you compare numbers.
Pair this with the calories burned walking calculator when you need the fuller picture.
Frequently asked questions
- What is 100 calories in joules?
- 100 cal equals 418.4 J (100 × 4.184).
- What is the calories to joules formula?
- J = cal × 4.184.
- How many joules are in a food Calorie?
- One food Calorie (kcal) equals 1000 calories, or about 4184 joules.
- How do I convert joules back to calories?
- Divide by 4.184, or use the joules to calories calculator.
- Which calorie does this use - thermochemical or International Table?
- It uses the thermochemical calorie, defined as exactly 4.184 J, which is the standard in chemistry and nutrition. The older International Steam Table calorie is 4.1868 J, so results differ by about 0.1% - negligible for food, but worth checking in engineering work.