What are kilojoules?

Kilojoules (kJ) are a way to measure energy. In Australia, the energy you get from food and drink and the energy your body uses is measured in kilojoules.

Energy can also be measured in kilocalories, also known as ‘calories’. One kilocalorie is the same amount of energy as 4.2 kilojoules.

How do kilojoules affect my body?

Your body needs energy 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 you use 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 a day to maintain a healthy weight. This can vary — some people need more, and others need 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 want to lose body fat to reach a healthy weight, you will need to take in fewer kilojoules than your body needs. You can talk to your doctor or a dietitian to help you reach a healthy weight.

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

Physical activity

When you are active, you burn energy. This includes:

• exercise
• manual work
• walking around
• small movements like fidgeting
• any other way you move your body

You can increase how much energy you use by being more physically active.

For example, if you take public transport for a day, you will likely burn more kilojoules than if you took a car. This is because you likely will have to walk further at each end of the trip.

Muscle mass

The more muscle you have, the more energy you will need.

How much muscle you have is influenced by your:

• 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 compared to adults. They need this extra energy to grow.

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

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

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

You can find out how many kilojoules are in the foods you buy from the nutrition information panel on food labels.

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

Some food labels also include the kilojoules by ‘serving’. Make sure you check what the manufacturers say a serving is, as it might be different from what you eat. The size of the serving will be listed. Serving 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?

If you are eating the right number of kilojoules for you, it is a good start, but it may not be a healthy diet. It’s also very important that you choose foods that contain all the nutrients that your body needs.

It’s good to keep in mind that 2 foods might have the same number of kilojoules, but differ in size and nutritional value.

For example, a large salad might contain the same number of kilojoules as a small block of chocolate or a small glass of lemonade. However, the salad will be more nutritious for you and will keep you feeling full for longer.

Resources and support

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

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.

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available to speak with you 24 hours a day, 7 days a week.