Calories ⇄ Kilojoules Converter

Convert food energy between kcal and kJ

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Calories ⇄ Kilojoules Converter

Food energy is shown in kilocalories (kcal, usually written as "Calories") in the US, UK and much of the world, but in kilojoules (kJ) in Australia, New Zealand and on EU labels. This converter switches between the two using the exact factor 1 kcal = 4.184 kJ, so you can read any nutrition label or recipe in the unit you know. Enter a value and choose which unit it is in to get the equivalent at once.

Conversion: 1 kcal = 4.184 kJ. Food energy is labelled in kilocalories (kcal, often just "Calories") in the US and many countries, and in kilojoules (kJ) in Australia, New Zealand and the EU (alongside kcal).

Putting the number in context

A 2,000 kcal day is 8,368 kJ, and the 8,700 kJ figure printed on Australian packaging is 2,079 kcal — that is the reference daily intake those labels are built around. European labels list energy per 100 g and per portion, so convert the line that matches what you will actually eat rather than the round 100 g figure, which is usually smaller than a real serving.

How to use this kcal to kJ converter

Value: 100 kcal → Convert → 418.4 kJ. Value: 418.4 kJ → Convert → 100 kcal. 1 kcal = 4.184 kJ.

Where the 4.184 factor comes from

One thermochemical calorie is defined as exactly 4.184 joules, so a kilocalorie is exactly 4.184 kilojoules — the factor is a definition, not a measurement, which is why the conversion is exact rather than approximate. An older International Steam Table calorie equals 4.1868 J, a difference of about 0.04 percent that never matters for food. The capital-C Calorie on a US label is one kilocalorie, or a thousand small calories.

Limits and practical tips

Label energy is not measured food by food: it is calculated with Atwater factors of roughly 4, 4 and 9 kcal per gram of protein, carbohydrate and fat, so the printed figure is a good estimate rather than an exact value for your plate. Regulators also allow rounding tolerances, and the EU counts fibre at 2 kcal per gram while US rules treat it differently, so the same food can legitimately differ between labels. To turn these numbers into a daily target, use our TDEE and calorie deficit calculators — and the CaloNote app logs the food itself from a photo.

Frequently Asked Questions

What is the difference between calories and kilojoules?
Both measure food energy. The kilocalorie (kcal, often just called a calorie) is common in the US, while the kilojoule (kJ) is the metric unit used in much of the world. One kcal equals 4.184 kJ, so they describe the same energy in different units.
How do you convert calories to kilojoules?
Choose whether you are converting from kilocalories or kilojoules, enter the value, and press Convert. The calculator multiplies kcal by 4.184 to obtain kJ, or divides kJ by 4.184 to obtain kcal. For example, 100 kcal equals 418.4 kJ.
Why do food labels use different energy units?
It depends on the country's regulations. Australia and the EU show kilojoules (the EU shows both), while US labels show calories. The converter lets you compare products across labels by translating any value to the unit you are familiar with.

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