Understanding kilojoules How to tell the difference between calories and kilojoules February 10 2021
Tracy McBeth Tracy McBeth Journalist

What’s the difference between calories and kilojoules? And how much energy should we consume each day? These basic tips may help cut the confusion.

We hear a lot about calories and kilojoules, but how do we read these numbers and use them to help with weight management and overall 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

Try our calorie converter.

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

What is a kilocalorie?

If calories and kilojoules weren’t confusing enough, enter the kilocalorie.

One ‘upper case C’ Calorie is a kilocalorie – which is actually 1000 ‘lower case c’ calories.

One kilocalorie equals 4 kilojoules (rounded to the nearest whole number).

Fortunately, the term kilocalorie is rarely used, but if you read a food label that seems too good to be true – check if it’s a lower case ‘c’. If so, it’s likely to be a kilocalorie.

How many kilojoules do you need each day?

The average Australian adult consumes about 8700 kilojoules per day. You get this energy from eating and drinking and use it for your body to function e.g. for breathing, blood circulation, digestion and exercise.

The 8700kJ is a rough guide for how much energy you’ll need to help maintain a healthy weight. Your individual need will depend on your sex, age or life stage (if you’re growing or pregnant you’ll need more), height, weight and how much physical activity you do. A male manual labourer in his 20s, for instance, will have a much higher energy need than a sedentary woman in her 70s.

Managing energy intake for a healthier weight

Weight management involves balancing your energy intake and physical activity. Generally, if we eat too many kilojoules compared to how much we burn in body functions and physical activity, the left-over energy that our body doesn’t use is stored as fat. If we eat fewer 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 try to have about 2000kJs difference between your energy intake and amount you use.

“Aim to lose no more than half a kilogram a week. If you’re losing weight quickly it might look great to start with, but then you 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. He suggests choosing quality low-GI carbohydrates that help keep you fuller for longer so you’re less likely to snack on unhealthy foods. Green also recommends increasing your activity by taking a walk at lunchtime or scheduling in regular exercise sessions.

A sugary drink

What are ‘empty calories’?

When it comes to calories and kilojoules, quality matters. 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 small 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 liquids aren’t going to fill you up in the same way,” he says.

Kilojoules should be a guideline only

Green says calories and kilojoules should be used as guides in conjunction with a healthy balanced diet.

“I think it’s a good thing for people to be aware of when 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.”

* The calorie converter 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 about diet and weight management as related to these calculations of calories and kilojoules.

Woman in supermarket looking at food Understanding kilojoules Dietitian Health Coaching Dietitian Health coaching offers Bupa members over-the-phone personalised nutrition coaching with a qualified dietitian, where you’ll choose a nutrition area you want to focus on. Learn more
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Tracy McBeth Tracy McBeth Journalist Tracy is a journalist with a passion for promoting good health; both mentally and physically.