How to tell the difference between calories and kilojoules

We often see either calories or kilojoules mentioned on the back of food packets, but do you know the difference between them?

It's important to be able to understand how to read these numbers so you can use them to help with weight management and your overall health.

Kilojoules (kJ) are the standard way of measuring your energy intake (what you eat and drink) in Australia.

A calorie is essentially the same thing on a different scale, just like the difference between inches and centimetres.

1 kJ = 0.2 calories

or

1 calorie = 4.2 kJs

Try our calorie converter.

*This calculator has been reviewed by Bupa health professionals and is based on reputable sources of medical research. It is not a diagnostic tool and should not be relied on as a substitute for professional medical or other professional health advice.

A kilocalorie (kcal) is equal to 1000 calories. Sometimes it can be called a Calorie (with a capital C). If you see a food label that seems too good to be true, then check whether the word has an upper case or lower case ‘c’.

The average Australian adult needs around 8,700 kilojoules per day.¹ This energy is used by your body to help it function. You need energy for everything from breathing and blood circulation, to digestion and exercise.

Your individual kilojoule needs will depend on your sex, age, weight, the amount of physical activity you do, and your life stage; if you're growing or pregnant, you'll need more. For example, a male manual labourer in his 20s will have much higher energy needs than a sedentary woman in her 70s.

Weight management involves balancing your energy intake with your energy expenditure. When you eat more kilojoules than you burn in bodily functions and physical activity, the leftover energy that your body doesn't use is stored as fat.

If you eat fewer kilojoules than your body needs to fuel daily tasks, then existing fat stores are tapped into, and you can lose weight.

If you want to lose weight, the ideal discrepancy between your energy intake and usage is around 2,000 kJ a day.

"Aim to lose no more than half a kilogram a week," advises Bupa Dietitian Nick Green. "Any more than that and you could fall into the trap of losing a lot of weight fast, then putting it back on again."

To lose weight sustainably, the key is to make simple changes that fit into your lifestyle. Low GI carbohydrates help keep you fuller for longer so you're less likely to snack on unhealthy food. If you need to increase your activity levels, add small amounts of exercise into your day, such as a walk at lunchtime or incidental exercise.

The term 'empty calories' or 'empty kilojoules' refers to foods and drinks that are high in energy, but that don't nourish our bodies or sustain us for a long period.

Alcohol or sugary drinks are a good example of this. "One standard alcoholic drink can contain around 290 kJ, so a couple of wines could have the equivalent energy of a small meal," says Green.

Supposedly 'healthy' drinks such as juices and smoothies can also add a lot of extra kilojoules into our diet. "Try and eat your kilojoules rather than drinking them," advises Green. "Liquids won't fill you up in the same way."

Calories and kilojoules should be used as guides in conjunction with a healthy balanced diet. "They are a good thing for people to be aware of when thinking about the different meals they eat," says Green.

However, it's important not to cut out nutritious foods such as nuts, fatty fish, olive oil and avocado just because they're higher in energy. "Healthy fats are an essential part of your diet."

Nutrition Australia offers information, advice and free resources on healthy eating.

Drinkwise has advice around drinking alcohol and how it can affect all areas of your health.