Kilocalories to Kilojoules
Convert kilocalorie to kilojoule instantly — type a value and read the result, with the exact formula shown.
Example
1 kcal = 4.184 kJ, 5 kcal = 20.92 kJ, 10 kcal = 41.84 kJ.
How it works
Kilojoule = Kilocalorie × 4.184. Every value is converted through a single joule base unit using internationally defined conversion factors, so any from/to pair stays consistent.
Good to know
Converting kilocalories to kilojoules is something most people run into when reading food labels. In the United States, energy on packaging is printed in "Calories" (which are really kilocalories), while Europe, Australia, and most of the rest of the world list energy in kilojoules — and many labels show both side by side. If you track your diet with an app set to metric units, or you're comparing an American product to one sold in the EU, this conversion turns one number into the other.
Both units measure the same thing — energy — but they come from different traditions. The calorie was originally defined around how much heat raises the temperature of water, while the joule is the SI (metric) unit of energy, named after physicist James Prescott Joule. Because a "dietary calorie" is actually 1,000 small calories (one kilocalorie), it lines up directly with the kilojoule, and the two are bridged by a single fixed factor.
The rule of thumb is simple: multiply kilocalories by roughly 4.2 to get kilojoules. So a 250 kcal snack is about 1,046 kJ, and a quick mental shortcut is "just over four times." To reverse it, divide kilojoules by 4.2. If you want to be precise, the exact factor is 4.184.
- The 4.184 figure is the thermochemical calorie, which nutrition labels worldwide use by international agreement — so this is an exact, not approximate, definition.
- Don't confuse the food Calorie (capital C, a kilocalorie) with the tiny physics calorie; a label's "120 Calories" means 120 kcal, which is 502 kJ, not 0.5 kJ.
Frequently asked questions
How do you convert kilocalorie to kilojoule?
Multiply the number of kilocalories by 4.184 to get kilojoules. For example, 1 kcal = 4.184 kJ.
What is 1 kilocalorie in kilojoules?
1 kilocalorie equals 4.184 kilojoules (1 kcal = 4.184 kJ).
How many kilocalories are in 1 kilojoule?
There are 0.2390057 kilocalories in 1 kilojoule.
Is this converter free and private?
Yes. It runs entirely in your browser, so your inputs never leave your device, there is no sign-up, and it works offline once loaded.
Are the conversions exact?
Conversions use internationally defined factors and are exact where the definitions are exact (for example, 1 inch = 2.54 cm). Displayed results are rounded for readability.
People also ask
How many kilojoules are in 100 kcal?
100 kilocalories equals 418.4 kilojoules. Multiply the kcal figure by 4.184 to get the answer.
Why do food labels show both kcal and kJ?
Many countries, including those in the EU and Australia, legally require energy to be listed in kilojoules as the official SI unit, while kcal is kept because consumers are familiar with it. Showing both lets shoppers in different regions read the label easily.
Is a kilocalorie the same as a food Calorie?
Yes. The 'Calorie' with a capital C on nutrition labels is a kilocalorie. So 200 Calories equals 200 kcal, which is 836.8 kJ.
What is 2000 kcal in kilojoules?
2000 kilocalories equals 8,368 kilojoules, since 2000 multiplied by 4.184 is 8,368. This is roughly the daily energy reference intake for an adult.
How do I convert kilojoules back to kilocalories?
Divide the number of kilojoules by 4.184. For example, 500 kJ divided by 4.184 equals about 119.5 kcal.
Why is the conversion factor 4.184 and not 4.2?
4.184 is the exact thermochemical calorie definition adopted internationally for nutrition. The value 4.2 is just a rounded version useful for quick mental math.
How many kJ is one slice of bread at about 80 kcal?
Around 80 kcal converts to roughly 335 kilojoules (80 multiplied by 4.184 equals 334.7 kJ).
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