What are the differences between Calories, calories, and kcals?

Why do we have different terms to describe the same concept?

In what cases is it useful to use one unit of measurement over the other?

  • 1
    I just found this out now. This is really bad science and the health science community should be ashamed of themselves.
    – user12335
    Dec 6, 2014 at 10:57
  • I am still not sure what the difference is between kcal and calorie. The explanations seem to say they are the same ...if that is true, why the long explanation?
    – user16176
    Jul 2, 2015 at 4:19
  • 1
    @Rose Food packaging uses 'calories' as the label when they really should use 'Calories' (ie with capital C) or Kcal. Sep 8, 2015 at 16:22

4 Answers 4


One calorie (with a lower case c) is the amount of energy required to heat 1 gram of water by 1°C. A kilocalorie is 1000 calories, and Calorie (with a capital C) and kilocalorie (Kcal) are synonyms. On food labels, nutrition facts are in terms of kilocalories/Calories. (Wikipedia)

Just like with grams vs. kilograms, units are used in a way that the number most readable. Putting nutrition labels in calories would take up quite a bit of extra space. I'm not sure how the Calorie/kilocalorie synonym came about, but I can guess it was for convenience. We use kilocalories much more frequently than calories for every day measurement, and kilocalories is quite a cumbersome word.

  • Right. The physics calorie (little "c" = 4.187 Joules) is an inconveniently small unit for talking about fueling the human body. Mar 30, 2011 at 21:54
  • 1
    quora.com/… answer suggests originally Calorie was intended to be the energy that it takes to heat 1 kg of water by 1C, but when converting to joules it is more convenient to use one thousandth of that value, so scientists redefined calorie to mean the energy it takes to heat 1g of water by 1C. Scientists and European standards adopted this definition, hence why food labels say kcal, but Americans and speech didn't adopt this
    – Steve
    Jan 6, 2019 at 14:59

It is still confusing, because both terms (with and without the kilo- prefix) covers the same amount, and it is only a capital letter that differentiates beween 1 and 1000.

This would be equal to having Gram (with a capital letter) and kilogram being the same, and gram being 1/1000 of that. I hopy everyone can see how stupid that would be, and this is exactly how stupid the Calorie term is.

There should only be calories and kilocalories. Calories (with a capital letter) does not fit in.

Besides, most food products list the energy contents at kcal and not Cal, which give the same short numbers. You never need to see 70000 instead of 70 even if Calories are dropped.

  • 1
    Luckily the difference is 3 orders of magnitude and therefore quite hard to not recognize when the wrong unit is used. That is to say, if something said "you should get 400,000 Calories from fat"… it's pretty obvious that should be 400,000 calories or 400 Calories or 400 Kcal. If the difference were a single order of magnitude, that would be confusing. This? Once you know it, you'll never be confused. Apr 30, 2018 at 18:39

A kilocalorie is equal to 1000 calories. I discovered this a while back. Although the labels on food packages display energy as calories, the actual metric is supposed to be kilocalories.

So that apple you may have just ate has 70000 calories or 70 kilocalories.

  • 3
    That's what you get if you don't use the metric system :P A kilometer is 1000 meters, a kilogram is 1000 grams. Simple huh? Btw your answer doesn't address Calories, with a capital C.
    – Ivo Flipse
    Mar 30, 2011 at 17:24

The mathematical sum of Cal versus Kcal

Small & large calories Small calorie (cal) is the energy needed to increase 1 gram of water by 1°C at a pressure of 1 atmosphere. Large calorie (Cal) is the energy needed to increase 1 kg of water by 1°C at a pressure of 1 atmosphere. Large calorie is also called food calorie and is used as a unit of food energy. cal to kcal - small calories to small kilocalories 1 kcal = 1000 cal The energy in small kilocalories (kcal) is equal to the energy in small calories (cal) divided by 1000: E(kcal) = E(cal) / 1000 Example Convert 6000cal to small kcal: E(kcal) = 6000cal / 1000 = 6 kcal Cal to kcal - large calories to small kilocalories 1 kcal = 1 Cal The energy in small kilocalories (kcal) is equal to the energy in large calories (Cal): E(kcal) = E(Cal) Example Convert 6Cal to kcal: E(kcal) = 6Cal = 6kcal

This should explain all, Questions? ....surely not!

  • 3
    Decent technical answer, but it duplicates what is already here, and is more confusing to read due to a lack of breaks in the sentences. Jan 30, 2017 at 15:35

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