What are kilojoules?

Kilojoules (kJ) are a way to measure energy. The energy you get from food and drink and the energy your body uses can both be measured in kilojoules.

In Australia, energy is measured in kilojoules. Energy can also be measured in kilocalories, or you might be more familiar with the term ‘calories’. One kilocalorie is the same amount of energy as 4.2 kilojoules. You can convert calories to kilojoules using the online calculator.

How do kilojoules affect my body?

Your body needs energy in order to function and move. If you take in more kilojoules from food and drink than your body uses, you store the extra energy as fat. If your body uses more kilojoules than you take in, you lose fat. If you take in the same amount of energy as your body uses, your weight will stay the same.

How many kilojoules do I need?

The average adult needs about 8,700 kilojoules (kJ) a day to maintain a healthy weight. But it varies quite a bit — some people need more and others less.

Many factors influence how much energy you need, such as:

• how active you are
• how much muscle you have
• your stage of life
• your age, sex, height and weight

If you would like to lose body fat in order to reach a healthy weight, you will need to take in fewer kilojoules than your body needs.

You can use this calculator to work out approximately how many kilojoules you need each day.

Physical activity

Movement burns energy. This includes exercise, manual work, walking around, small movements like fidgeting and any other way you move your body.

You can increase how much energy you use by being more active. For example, if you use public transport for a day, you are likely to burn more kilojoules than if you use a car, because you probably have to walk a distance at each end of the trip.

Muscle mass

More muscle needs more energy. How much muscle you have is influenced by:

• age — most people have less muscle as they get older
• sex — most males have more muscle than most females
• height
• body build

Stage of life

Children and adolescents need to take in more energy in their food, as they are growing.

If you are pregnant, you will need to take in about 1,400 kJ extra per day in the second trimester and about 1,900 kJ extra per day in the third trimester to nourish your baby.

If you are breastfeeding, you will need to take in more energy in order to produce milk — about 2000 kJ extra per day if your baby is fully breastfed.

How do I know how many kilojoules are in foods and drinks?

Food and drinks provide the energy you need to stay alive and active. You can work out how many kilojoules are in the foods you buy by looking at the nutrition information panel on food labels.

By law, food labels must list the kilojoules in 100g of a product (or 100mL for liquids). In some states and territories, certain food retailers are required to display the kilojoule content of their food and drinks at point of sale.

Some also include the kilojoules in a ‘serving’. Be aware that what the manufacturers say is a serving might be different from what you eat. The size of the serving will be listed — the size will be different for different products.

You can find out the number of kilojoules in many foods including fresh fruits and vegetables on the Food Standards Australia and New Zealand food composition database.

Vegetables and many fruits are generally quite low in energy. Fast foods, fried foods and products such as cakes, desserts and pastries have much more energy.

Is my diet healthy if I eat the right number of kilojoules?

Eating the right number of kilojoules for you is a good start, but it’s not the only measure of a healthy diet. It’s also very important to choose foods that contain all the nutrients that your body needs.

Keep in mind that 2 foods might contain the same number of kilojoules, but their size and nutritional value may be very different. For example, a large salad might contain the same number of kilojoules as a small block of chocolate or a small glass of lemonade, but the salad will be more nutritious and keep you feeling full for longer.

Resources and support

If you would like more information, the Australian Dietary Guidelines give advice on eating for health and wellbeing.

Use this calculator to work out approximately how many kilojoules you need each day.

You can find out the number of kilojoules in many foods including fresh fruits and vegetables on the Food Standards Australia and New Zealand food composition database.