In the United States, virtually every food that I buy from a grocery store has Nutrition Facts on it that contain the calorie count on it. For instance, the label on a granola bar might say that it has 150 Calories.

According to Wikipedia, a Calorie (with a capital C, also called a kilocalorie) is the amount of energy needed to raise the temperature of one kilogram of water by one degree. However, it's not clear to me how companies would figure out how this translates to the Calorie count of their granola bar. I presume they don't just incinerate the food. Also, I'm guessing that they could ship off packaged foods somewhere to have it measured, but that wouldn't work for restaurant prepared foods.

There was a similar question titled How to calculate the calorie content of cooked food?, but it was focused on home food and relied on estimation. I presume that companies need to be much more precise in order to meet regulations.

So how do companies find out how many calories are in their food?

  • Possible duplicate of Calculating Nutrition Information for Commercial Food Labeling
    – TFD
    Nov 4, 2015 at 8:53
  • @TFD I don't think this is a duplicate. I'm more interested in how they figure out how calories are determined in the first place, not how it can be plugged into Wolfram Alpha to create a nutrition label. Nov 4, 2015 at 19:31
  • Sorry, you may have misunderstood. That is one of the valid resource companies use. Wolfram sells expensive but accurate data sets sourced from scientific and government researchers around the world. wolframalpha being free to basic users is his giveback to humanity :-)
    – TFD
    Nov 4, 2015 at 20:04
  • @TFD It's helpful to know that Wolfram Alpha is a helpful repository, but I am also interested in how those numbers are determined in the first place. Fortunately, the answers in this question seem to answer that. Nov 4, 2015 at 20:14

2 Answers 2


These days, mostly software. In the good/bad old days, by actually burning it (or having a laboratory do that for them). Software is much simpler (unless you are writing it, though it is probably more tedious than complex.)

Input ingredients and quantities, out comes calories. For a restaurant that assumes that the recipe used for calculation matches the actual recipe used.

Here is a USDA database, for instance. Tedious to use, but gives the idea. http://ndb.nal.usda.gov/ndb/nutrients/index

  • 1
    So does the software get its numbers? By recording data from the old days of burning? And does the software need to take into account changes in composition due to cooking and other things? Nov 4, 2015 at 3:25
  • 3
    AIUI, using standard data from calorimetery, and changes in composition have no effect on calories. i.e., short of burning the food beyond the point where anyone's going to eat it, cooking does not alter the caloric content of ingredients.
    – Ecnerwal
    Nov 4, 2015 at 4:20
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    That's one reason why the whole idea of calories counting is totally flawed: a bag of coals gives a great nutritional value in a caloriemeter, but not when people eat the coals. People are not ovens.
    – Robert
    Nov 4, 2015 at 15:50

Initially this was done through experimentation, a substance of an exact mass will always produce the same amount of heat when burned.

This was upgraded through chemistry to get this as accurate as at the molecular level. Then all you need to know is how much of this stuff so I have? to get an answer.

So when you have a recipe, you can add up all the calories you have and subtract anything that removes or burns calories in the processing (endothermic reactions for example consume material and transform some of that into heat which is calories burned).

Then also there is dietary science. Some stuff simply isn't digested. For loose example, a calorie of dietary fiber does not contribute to your caloric intake because it simply passes through the body untransformed and unabsorbed.

Nowadays, most of this information is kept in public ally accessible databases.

  • Dietary science doesn't matter. The labels denote what's in the food, not what your body is going to use out of it.
    – rumtscho
    Nov 4, 2015 at 17:24
  • 2
    is that true? Cellulose is just a polysaccharide and as such has energy similar to starches but are inaccessible to humans - you can burn a log of wood but you shit any wood you eat.
    – worthwords
    Nov 11, 2015 at 0:00

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