Just like yards became metres and pounds became grams, so Calories have become kilojoules. Kilojoules are the metric equivalent of Calories and have replaced Calories in Australia and many other metric countries. Yet they're very confusing, especially to my US visitors who have always only known Calories (lucky for me, I grew up with Calories then had to learn kilojoules!)
These are the units used to measure food energy - kilojoules (abbreviated to kJ) and Calories (Cals). Like other food scientists, I use the capital C as shorthand for the longer correct term of kilocalories.
Kilojoules LOOK four times larger than Calories simply because there are more digits eg a bowl of cereal supplies around 480 kilojoules or 117 Calories.
Conversion is 4.2 ... or just 4
1 Calorie equals 4.186 kilojoules (4.2 or simply 4 is close enough for a quick conversion).
For example, a slice of bread supplies 290 kilojoules or (290 divided by 4) 70 Calories.
Kilojoules are difficult to grasp if you don't have a feel for the numbers. So here's a handy guide to make things more ‘friendly'.
|kJ||Cals||Intake or level|
|10000||2400||Typical level of intake of most teenagers|
|8700||2070||Average intake used to calculate %DI on food labels|
|7500||1800||Typical weight loss level for a moderately-active man|
|7000||1650||Typical weight loss level for a sedentary man|
|6000||1500||Typical weight loss level for a moderately-active woman|
|5000||1200||Typical weight loss level for a sedentary woman|
Supervised fast or meal replacement intake
Here's how food compares in kilojoules and Calories:
|Canned salmon, drained||1 can||150g||525||125|
|Tim Tam chocolate biscuits||2||38g||840||200|
Krispy Kreme doughnuts, original glazed
|Orange juice||1 glass||250ml||400||95|
1 glass orange juice = 400kJ or 95 Calories
Round the kilojoules to the nearest 0 or 5. So 288kJ rounds up to 290kJ while 292 rounds down to 290kJ. Five kilojoules translates to 1 Calorie which is hardly anything and makes your useage of kilojoules easier as there's fewer digits to remember. We round off all the kilojoule counts on our recipes for ease of use - see here.
Rule of thumb
To obtain Calories, divide kilojoules by 4 for a quick conversion.