How to Tell the Difference Between Calories and Kilojoules

What’s the difference between kilojoules and calories? And how much is too much energy to be eating? These basic tips may help cut the confusion.  

We hear a lot about kilojoules and calories, but how do we use these facts and figures to help manage our weight and stay in good health?

What are kilojoules?

Kilojoules or kJ are how we measure our energy intake (what we eat and drink) in Australia.

A Calorie is essentially the same thing, but the scale is different. Just like the difference between inches and centimetres. 

1 kJ = 0.2 Calories 


1 Calorie = 4.2 kJs

Enter the value in calories to calculate in kilojoules, or enter a value in kilojoules to convert to calories.


Learn more about the calorie converter

One ‘uppercase C’ Calorie is actually a kilocalorie (1000 ‘lower case c’ calories) and equals 4 kilojoules (rounded to the nearest whole number).

This tool has been reviewed by Bupa health professionals and is based on reputable sources of scientific evidence. It is not diagnostic and should not be relied on as a substitute for professional medical or other health professional advice. Consult your doctor if you have questions.

Up next: How to tell the difference between calories (cal) and kilojoules (kJ)

How many kilojoules do you need each day?

The average Australian adult energy intake for weight management is about 8700 kilojoules per day. You use this energy from what we eat and drink for your body to function e.g. for breathing, blood circulation, digestion and exercise.

The 8700kJ amount is only a rough guide for how much you need in your food and drink to help maintain a healthy weight. How much you need personally will vary depending on your sex, age or life stage, height, weight and how much physical activity you do.

Managing kilojoule intake for a healthier weight

Generally, if we eat too many kilojoules compared to how much we use in physical activity, the left over energy that our body doesn’t use is stored as fat. If we eat less kilojoules than our body needs to fuel daily tasks, then existing fat stores are tapped into, and we can lose weight.

Bupa dietitian Nick Green says if you want to lose weight look to have about 2000kJs difference between your energy intake and amount you use.

“Aim for no more than half a kilogram a week, anything more if you’re losing weight quickly it might look great to start with, but then it could fall into the yoyo trap if you’re making big changes and seeing rapid weight loss,” says Green.

Green says the key is to make simple and sustainable changes that fit into your lifestyle, from choosing quality low-GI carbohydrates to help keep you fuller for longer so you’re less likely to snack on unhealthy foods, to getting more activity into your day by taking a walk at lunch or fitting in regular exercise sessions.

sweet drinks

What are ‘empty calories’?

The term ‘empty calories’ or ‘empty kilojoules’ refers to things we consume that are high in energy, like alcohol or sugary drinks, that don’t nourish our bodies or sustain us for a long period.

“If you’re having one standard drink it could contain about 290kJ, so a couple of wines could have the equivalent energy of a smaller meal,” says Green.

Green says sugary ‘healthy’ drinks including some juices and smoothies can add a lot of extra kilojoules into our diet too.

“I talk to people about eating your food instead of drinking it because it’s not going to fill you up the same,” he says.

Kilojoules should be a guideline only

Green says kilojoules should be used as a guide in conjunction with a healthy balanced diet.   

 “I think it’s a good thing for people to be aware of, thinking about the different meals they eat,” says Green.

However he says it’s important not to discount certain nutritious foods like nuts, fatty fish, olive oil and avocado just because they’re higher in energy.

“You shouldn’t avoid something like a can of tuna which contains healthy fats, which is extra energy, because it has also got a lot of protein and other good stuff.”

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