Quick answer
There are 4.184 kJ in one calorie (kcal). Turned around, 1 kJ is 0.239 kcal. If you mean the small calorie (cal), there are 0.004184 kJ in one cal.
How many kJ to a calorie?
How many kJ to a calorie depends on the size of the calorie. Food labels use the kilocalorie, written kcal and often called simply "calorie" or "Cal".
| Unit | In kilojoules | In joules |
|---|---|---|
| 1 calorie (kcal, food Calorie) | 4.184 kJ | 4,184 J |
| 1 small calorie (cal) | 0.004184 kJ | 4.184 J |
| 1 kilojoule (kJ) | 1 kJ | 1,000 J |
So if someone asks how many kJ to cal on a food label, the number to remember is 4.184.
What is kJ to cal?
"What is kJ to cal?" is a shortcut for "how do I change kilojoules into calories?" The answer is one division: kcal = kJ ÷ 4.184. Use the KJ to Cal converter to do it instantly, or read the step-by-step method.
What is kJ to calories in everyday numbers?
What is kJ to calories in practice? Here are some familiar round numbers:
| Kilojoules | Calories (kcal) | Small calories (cal) |
|---|---|---|
| 100 kJ | 23.901 kcal | 23,900.6 cal |
| 500 kJ | 119.5 kcal | 119,502.9 cal |
| 1,000 kJ | 239.01 kcal | 239,005.7 cal |
| 2,000 kJ | 478.01 kcal | 478,011.5 cal |
| 8,700 kJ | 2,079.35 kcal | 2,079,349.9 cal |
kJ is how many calories?
Ask "kJ is how many calories?" and the answer is that a single kilojoule is 0.239 kcal, or 239.006 small calories. Because a kilojoule is a smaller unit, you always end up with a smaller number of kilocalories than kilojoules. See the 1 kJ to calorie page for the working.
What is kJ in calories on a food label?
What is kJ in calories on a packet? Many labels show both, for example "1046 kJ (250 kcal)". If your label only shows kJ, divide it by 4.184. If it only shows calories, multiply by 4.184 to see the kJ.
kJ in cal, kJ in calorie and kJ in calories
You will see the same idea written in several ways: kj in cal, kj in calorie and kj in calories. The best mental picture is a ratio. Every calorie contains 4.184 kJ, so any number of calories contains 4.184 times as many kJ. The reverse holds for calories in a kJ: each kJ contains only 0.239 of a calorie.
Why is the number 4.184?
The calorie was first defined by the heat needed to raise the temperature of water. Modern science uses the joule, and the thermochemical calorie is now fixed at exactly 4.184 joules. That is why our converter and every nutrition source treat the ratio as exact. The full story is in what is a calorie and what is a kilojoule.
Frequently asked questions
How many kJ are in a calorie?
One calorie (kcal) is 4.184 kJ. One small calorie (cal) is 0.004184 kJ.
How many calories are in a kJ?
One kJ is 0.239 kcal, or 239.006 small calories.
Is 1 kJ the same as 1 calorie?
No. 1 kJ is less than a quarter of a calorie (kcal). You need 4.184 kJ to equal one calorie.
How many kJ are in 100 calories?
100 calories (kcal) is 418.4 kJ. See 100 calories to kJ.
Last updated 11 Oct 2026. How we calculate.