How to convert kilojoules to calories

Written by Catherine Saxelby on Wednesday, 30 September 2009. Posted in Measures and conversions
Tagged: calories, conversions, dieting, diets, energy, fat loss, food labels, FSANZ, kilojoules, nutrients, technology

How to convert kilojoules to calories

 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 almost all 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). Kilojoules are four times larger than calories 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'.

How diets compare in kilojoules and calories
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
4000 1000

Supervised fast or meal replacement intake

- too low for normal activity

 

Here's how food compares in kilojoules and calories:

Various foods in kilojoules and calories
Food Amount grams kJ cals
Bread 1 slice 30g 290 70
Egg 1 large 60g 335 80
Canned salmon, drained 1 can 150g 525 125
Tim Tam chocolate biscuits 2 38g 840 200

Krispy Kreme doughnuts

(original glazed)

2 104g 1680 400
Orange juice 1 glass 250ml 400 95

 

orange-juice-smll1 glass orange juice = 400kJ or 95 calories

 

Tip

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.

Catherine Saxelby

About the Author

Catherine Saxelby knows nutrition! She is an accredited nutritionist, food commentator, blogger and award-winning author. Her latest book - Catherine Saxelby's Food and Nutrition Companion – answers all those tricky questions on healthy eating, diets and supplements. It draws together a lifetime of advice and gives you all you need to know to eat right!

Comments (4)

  • Ian Sinclair

    Ian Sinclair

    18 November 2013 at 15:47 |
    Dear Catherine,
    Found your web site very helpful and informative but unfortunately I must disagree with your formula for converting calories to kilojoules viz: 1 calorie = 4.186 kilojoules
    Actually 1 calorie = 4.186 joules (not Kilojoules)
    Or, 1 calorie = 0=004186 kilojoules
    You are not alone in making this mistake, every weight loss web site I have looked at contains the same error. Similarly, food packaging data makes the same error.
    Doesn't anyone in the food business know the difference between kilojoules and joules?
    I really would appreciate your comments if you have time.
    Yours faithfully,
    Ian Sinclair
  • Catherine Saxelby

    Catherine Saxelby

    26 November 2013 at 20:13 |
    I understand the confusion about calories and kilocalories! Why? Because although values are given in the number of kilocalories in a food, we call them simply ‘calories’. Sometimes you’ll see Calorie spelled with a capital C to denote that it’s been shortened. Sometimes older books use the term kcal.

    Regardless, in popular books, magazines and websites today, calories are used interchangeably with kilocalories.

    1000 calories = 1 kilocalorie = 1 Calorie

    Think if you converted grams to kg but then spelled the word with a capital G eg
    1000gram = 1 kilogram = 1 Gram

    Which explains why you are out by a thousand all the time.

    Your units should be:

    1 Calorie or kcal = 4.186 Kilojoules (note the capital C)

    Or

    1 calorie = 0.004186 kilojoules

    Does this help? Catherine
  • MurrayT

    MurrayT

    20 January 2014 at 19:55 |
    Catherine - you are right. People get confused between calories and Calories!

    MurrayT
    • Catherine Saxelby

      Catherine Saxelby

      20 January 2014 at 20:19 |
      Thanks Murray! Yes it IS confusing, isn't it? I'd like to start a campaign to go back to calories! Maybe it would mean more than kilojoules so people could 'recognise' how much they're eating? What do you think? Catherine

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