Quick answer
cal = J ÷ 4.184 and kcal = J ÷ 4,184. For example, 4,184 J is 1,000 cal, which is 1 kcal.
Joules to calories table
| Joules | Small calories (cal) | Kilocalories (kcal) |
|---|---|---|
| 1 J | 0.239 cal | 0.000239 kcal |
| 10 J | 2.39 cal | 0.00239 kcal |
| 100 J | 23.901 cal | 0.0239 kcal |
| 1,000 J | 239.01 cal | 0.239 kcal |
| 4,184 J | 1,000 cal | 1 kcal |
| 10,000 J | 2,390.06 cal | 2.39 kcal |
| 100,000 J | 23,900.6 cal | 23.901 kcal |
Worked example: heating a cup of water
Heating 250 g of water from 20 °C to 100 °C needs about 250 × 80 = 20,000 cal, since it takes about 1 cal to warm 1 g of water by 1 °C. In joules that is 20,000 × 4.184 = 83,680 J, or 20 kcal. Going back the other way, 83,680 ÷ 4.184 = 20,000 cal. This is how the calorie was first defined.
Joules, kilojoules and calories
A joule is small, so food and most household energy is given in kilojoules (1 kJ = 1,000 J). For food, use the KJ to Cal converter directly. For an overview of all three units, see kJ vs calories.
Frequently asked questions
How many calories are in a joule?
One joule is 0.239006 small calories, or 0.000239 kcal.
How many joules are in a calorie?
One small calorie is 4.184 joules. One kilocalorie is 4,184 joules.
what is a calorie in joules?
One small calorie (cal) equals 4.184 joules (J). This means that 1 joule is approximately 0.239 calories. To convert joules to calories, divide the energy value in joules by 4.184. For example, 100 joules equal approximately 23.90 calories. Our joules to calories converter makes this calculation simple and convenient.
Last updated 15 Oct 2026. How we calculate.