Ever looked at the nutritional label on a food package only to stare at a long list of numbers with no clue what they mean? All that data about kilojoules and calories can be pretty confusing. Are they the same thing? What does it mean for managing your weight? And how do you know how many kilojoules you need in a day?
We teamed up with dietitian, Rachel O'Connor, to cover all things kilojoules (kJ) and calories (cal) to help you stay fit, healthy and strong.
What are calories and kilojoules?
Calories and kilojoules are measurements for the amount of energy we get from food and drink. “When we talk about calories and kilojoules, we’re talking about the same thing – a measure of how much energy is in the foods and drinks we consume,” explains Rachel. “Just like when we compare a mile to a kilometre, calories are the imperial system, and kilojoules are the metric system.”
How do you convert kilojoules to calories?
Not all food labels list the kilojoule and calorie count of food. If you prefer to use one over the other, you’ll need to know how to convert them.
“Nutrition information panels for Australian products will always show the kilojoule content,” says Rachel. “However, international brands may show one or the other, depending on whether they use the metric or imperial system as a unit of measure.”
So, how many kJ in a cal? Well, one calorie is around four kilojoules. For a rough conversion when you’re out and about, divide the number of kilojoules by four to get the calories. To reverse it, multiply the calories by four to get the kJ.
If you want to get specific, Rachel explains that 1 calorie = 4.18 kilojoules. So, whip out the calculator on your phone or search for an online kJ converter to get the exact number.
How does understanding kilojoules help with weight management?
Your body needs energy to function, and it gets that energy through food. If you consume more kilojoules than your body uses, that extra energy might be stored as fat. But if you use more energy than the kJs you consume, you might lose fat. And if you consume and use the same amount of energy, your weight will stay the same. Knowing how much energy you both consume and use can help you manage a healthy weight through healthy meal and exercise planning.
What type of foods have high/low numbers of kilojoules?
All food and drink come with their own set of kilojoules. Here’s a very simple breakdown of what foods and drinks are high or low in kilojoules:
High: Food and drink high in fat, added sugar and alcohol tend to have the most kilojoules.
Moderate: Protein and carbohydrates provide a moderate amount of kilojoules, which are essential for varied diet.
Low: Fruits and legumes are lower in kilojoules and water has zero kilojoules.
Looking at the energy content of our food can be helpful, but it’s not the best way to check is something is 'healthy’.
“This is because not all food is created equal. Just because a chocolate bar might have a lower kilojoule content than a chicken and salad roll doesn’t mean that they are equally ‘healthy’. What makes the chicken and salad roll the healthier option is that it is high in fibre, nutrient-dense, low in saturated fat and provides better satiety.”
How do you work out your daily kilojoule needs?
The amount of energy you need each day comes down to your specific needs. The average adult needs about 8700kJ (or around 2080 calories) each day to maintain a healthy weight. But things like your activity levels, muscle density, age, gender, height and weight can impact how many kJ you need each day.
There are lots of online kilojoule calculators that can help you work out how much energy you need each day.
Why does Australia use kilojoules instead of calories?
Australian health recommendations and dietary guidelines use kilojoules, which is aligned with the International System of Units (SI). While New Zealand and much of Europe also use kilojoules, countries like the US and Canada requires kilocalories (often labelled as calories).
Are kilojoules or calories more accurate?
Neither form of measurement is more accurate than the other – they’re simply two different methods of measuring the same thing.
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