The joules to calories formula
To convert joules to calories, divide by 4.184: cal = J ÷ 4.184. For example, 1000 J ÷ 4.184 = 239.01 cal. One thermochemical calorie equals 4.184 joules exactly. To reverse it, use the calories to joules calculator.
More examples: 500 J ÷ 4.184 = 119.50 cal, and 3600 J — one watt-hour — is 860.4 cal. Because the factor is a division, a joule is always the smaller unit: any energy in calories is roughly a quarter of the same energy in joules.
How to convert J to cal
Enter an energy value in joules and the calculator divides by 4.184 to give small (gram) calories. Note that food labels use the large Calorie (kcal), which is 1000 of these calories, so 1000 J equals about 0.239 food Calories.
Where the two units turn up: joules are the SI unit used for work, heat and electrical energy, so lab data, physics problems and appliance ratings are in joules or kilojoules. Calories survive mainly in nutrition and in older heat-of-reaction tables. A 2000 kcal daily diet is 2000 × 4184 = 8,368,000 J, or 8368 kJ, which is why many food labels print both kJ and kcal.
The most common mistake is mixing the two calories. Lower-case cal is the small (gram) calorie; capital Cal or kcal is 1000 of them. If a result looks about a thousand times too big for a food value, you have the small calorie and need to divide by 1000.
People working on this usually reach for the kilowatts to horsepower calculator too.
Joules to calories reference table
| Joules | Calories |
|---|---|
| 1 J | 0.239 cal |
| 100 J | 23.90 cal |
| 1000 J | 239.01 cal |
| 4184 J | 1000 cal |
Pair this with the calories burned running calculator when you need the fuller picture.
Frequently asked questions
- What is 1000 joules in calories?
- 1000 J equals 239.01 cal (1000 ÷ 4.184).
- What is the joules to calories formula?
- cal = J ÷ 4.184.
- Are these the same as food Calories?
- No. Food labels use the large Calorie (kcal), which is 1000 small calories. Divide cal by 1000 for kcal.
- How do I convert calories back to joules?
- Multiply by 4.184, or use the calories to joules calculator.
- Which calorie definition does this use?
- The thermochemical calorie, defined as exactly 4.184 joules, which is the standard in chemistry and physics. Other historical definitions such as the 15 °C calorie (4.1855 J) and the International Table calorie (4.1868 J) differ by well under 0.1%, so results match to three significant figures.