Convert Calories to Kilojoules

Use these tools to change kilojoules to Calories (kJ to Cal), or calories to kilojoules. Dragging the SLIDER will convert the calories to kilojoules and vice-versa. Then, read on to learn all about calories versus kilojoules. Find out why food labels list kilojoules and energy rather than calories.

Read on to learn all about calories compared to kilojoules:

Kilojoules to Calories, kJ to Cal

Kilojoules and calories are different unit measures of the same thing, but even professionals get confused when trying to use one or the other or both at the same time.

Why Calories and Kilojoules?

Why do nutrition labels on food packages measure energy in kilojoules (kJ) instead of Calories (Cal)? Are they really the same thing? Why does it seem that there are thousands of kJ in foods but only hundreds of calories? Some people say kilocalories (kcal), whilst others say calories. Yet others insist on capitalising the “C” in in the word Calorie. How is is possible that some unit converters give wildly different results when changing kilojoules to calories compared to others? Why do we call ourselves Calorie Counter Australia instead of Kilojoule Counter Australia? So many questions, let’s get some answers!

Different units measure the same thing!

To be clear, for our purposes, both calories and kilojoules refer to the same thing: food energy.

Energy is the ability to do work.

Work is movement.

“Kilojoule”, and “calorie”, describes the amount of movement which food allows us to do! Read our home page to get a more detailed explanation of what, exactly, a calorie is.

kilojoules to calories in an egg
Calorie Counter Australia lists both Cal and kJ

Why have Kilojoules on food packaging?

Australian government regulations and standards call food energy “kilojoules” (abbreviated to “kJ”). However, this was not always the case, because from 1812 to the 1970’s, “calories” or “Cal” were used instead. 

The shift from calories to kilojoules was just another one of the things that changed when we adopted the SI metric measurement system. Parliament passed the Australian Metric Conversion Act in 1970, and government agencies therefore followed through shortly thereafter. 

That is why food packages list kJ instead of Cal today.

We still use calories!

We still use calories instead of kilojoules for two main reasons:

Reason 1 – for most of our nation’s history, calories is the word most people used (and still use). Even if you were born after 1974 when the big changes happened, it is likely that kJ have not replaced calories in your mind. A difference, which makes no difference, is not a difference!

Reason 2 – cultural transmission. Australia and New Zealand are arguably the only significant English-speaking countries to have officially opted for kilojoules over calories. That’s 30 million people supposedly saying “kilojoule”, versus 400 million saying “calorie”. As a result of almost every book, movie, TV show, podcast, webcast, song and article using “calories” rather than “kilojoules”, we do the same. 

Scroll to the bottom of this page to watch the music video “Kaluli”. This massive hit from China, performed by an energetic group, is about their futile attempts to avoid calories (“kaluli”). Tellingly, the Chinese word for food energy, derived from English, is “kaluli” rather than “kilojuli”. 

From this example of pop culture and many others, we can see that “calories” have seeped deeply into the world’s culture,  whereas “kilojoules” have not. 

Scientists Use Calories
Chemists use kcal

Scientists use Calories

Furthermore, even the international scientific community has stubbornly refused to give up the calorie. Despite the global adoption of the SI unit system for science research, it seems that the current method in chemistry is to use kilocalories rather than kilojoules.

Food energy is measured by using a device called a bomb calorimeter. There is an entire specialisation in science known as calorimetry. The World Health Organisation talks about Daily per Capita calorie supply, rather than Daily per Capita kilojoule supply.

Now you know why we call ourselves Calorie Counter Australia, rather than Kilojoule Counter Australia!

When is a calorie a kilocalorie?

Just as there are one thousand joules (J) in a kilojoule (kJ), there are one thousand calories (cal) in a kilocalorie (kcal). In other words, both the calories system of measurement and the joules system use decimals.

Here comes the the tricky part: the generally accepted convention is to call kilocalories “Calories”, with an uppercase “C”, whilst calories (one thousandth of a kilocalorie) keep their lowercase “c”. Since “Calories” sounds the same as “calories”, the two meanings often get mixed up and people do not use a capital “C”, even when they mean kilocalories rather than calories. The abbreviation for Calories/kilocalories is “kcal” or “Cal” whereas the abbreviation for calories is “cal”.

Conversion Confusion

This is why some unit conversion tools seem to offer wildly different results, depending on whether or not the users are expecting to see kilocalories or calories. Trying to convert 1,200 calories with one of those converters gives you the result 5 kilojoules, which is obviously wrong (5kJ is what is in one third of a gram of Weet-Bix).

To make things even more confusing, when most people talk about calories in food, they really mean kilocalories! That is, Calories rather than calories, kcal or Cal rather than cal. You’re on safe ground to assume that whenever the word “calorie” or the abbreviation “cal” is used in connection with food, the true meaning is kilocalories (kcal/Cal).   

convert kilojoules to calories
One Calorie has the same energy as 4.184 kilojoules

How to convert kilojoules to Calories kJ to Cal?

We convert kj to Cal and vice-versa by multiplying or dividing by the fixed conversion rate. One calorie (cal) is equal to 4.184 joules (J). This means that one Calorie/kilocalorie (Cal/kcal) is equal to 4.184 kilojoules (kJ).

The practical formula is:

E (Cal) = E (kJ) x 0.239

Sometimes, you will hear people say that, as a rule of thumb, just divide/multiply by 4 to get the calorie or kilojoule count. At Calorie Counter Australia, we insist on using the more precise 4.184 conversion rate, because 0.184 is over 4% of 4.184.   Whilst it may not sound like much, consider that 4% of a typical daily calorie intake could easily be 100 Calories. 100 Calories is about the amount of energy contained in a medium-sized banana.

Calories vs Kilojoules

Calories VS Kilojoules: Does it Really Matter?

Having covered the difference between kilojoules and calories, and figured out how to convert them, we can answer the question: does it matter which one we use? In theory, since both calories and kilojoules are standard units which measure energy, it ultimately should not matter. The most important aspect of both kilojoules and calories is that we can use either to record and compare the food energy we consume (or plan to consume) at any given time. Your choice will probably come down to these factors:


All physical food nutrition labels in Australia list food energy in kJ, and some list both kilojoules and Calories. Most digital (English language) resources list food energy in Calories, and some list both Calories and kilojoules. If you get most of your food energy information from physical labels, the kJ seems to be the way to go. If you get most of your food knowledge from digital sources, then Calories probably works better.


How easy is it for you to use the label to understand how much energy there is in each food? The nutrition label on packaged foods lists kilojoules per “serve” and kilojoules per 100g. Can you mentally or electronically (with the aid of a digital app) use the food label effectively, on a day-to-day basis? Can you perform the same task more easily using digital alternatives to the nutrition label? If you find the digital option to be more convenient, you will probably want Calories for reasons outlined above.


Is it easy to convert food energy units between kilojoules and Calories? How hard is to find a printed cross-reference table, or online conversion tool, or perform a mental calculation? If it is easy to convert between Cal and kJ and vice-versa, then perhaps either are equally appealing.


What food energy units are usually listed in your recipe book, website or app? It is easier to become comfortable with the predominant unit of measure over time, rather than having to do conversions for each prepared meal or individual ingredients.

Gym Equipment

If you have a gym membership, or own some modern gym equipment, chances are that it sports a “smart” panel which measures energy burned during your workout. Does the equipment display calories, kilojoules, or either?

All usage factors aside, it is most important to understand what both mean. Whichever unit of measure you opt for, use it to compare your food choices and monitor your food energy intake. Use our Calorie Tracker to do both, all you need is a free calcount account. Come back to this page when you want to convert calories to kilojoules!

Calories VS kilojoules in Popular Culture

The word “calorie” has seeped deeply into our global culture, in ways that the word “kilojoule” has not. Don’t believe us? Check this out:

This is an entertaining video about calories