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How can I calculate the Amount Per Serving label in the nutrition facts.

Not basing it as a recipe where it is already stated but by ingredients. For example, I have a customized recipe, I want to know the amounts per serving based on my ingredients.

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What countries labeling laws are you looking at? –  SAJ14SAJ Mar 7 at 13:29
    
If it's a custom recipe, just require it to include how many people it serves. –  Jefromi Mar 7 at 16:28
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Are you asking how to compute the serving size ("each serving is 1 cup") or the number of calories, etc. per serving? –  derobert Mar 7 at 16:43
    
@derobert The serving size, seems pretty clear from "amount per serving". He asked separately about the nutritional content. –  Jefromi Mar 11 at 15:03
    
also see cooking.stackexchange.com/q/42664/304 –  Kate Gregory Mar 11 at 17:20
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2 Answers 2

You set it arbitrarily, although hopefully based on some reasonable single portion size. Once you have the serving size, you calculate the nutritional information based upon it.

There is some rumor of stronger regulation forthcoming in the US to make portion size claims on labels more realistic, but that is not the case at this time.

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But to what do i base it from? Do i just add all the amounts per serving from all the ingredients and make that the new amounts per serving of the recipe? –  John the programmer Mar 7 at 10:57
    
You base it on judgment and knowledge... it isn't something you can automate. The unit even varies, portions of a whole (1/8 of a pie), cups (breakfast cereal), and so on. –  SAJ14SAJ Mar 7 at 10:59
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No such calculation exists. You cannot solve this problem programmatically. Even if the recipe includes a yield, "36 cookies", you would have to decide if the serving size is one cookie or three. –  SAJ14SAJ Mar 7 at 11:04
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The question doesn't say anything about a specific country, so the paragraph about forthcoming regulation doesn't seem relevant. –  Peter Taylor Mar 7 at 12:37
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I'm not saying US regulations apply everywhere. But if you're trying to make an informed guess for serving size, given a choice between "I have no information, I will do it alone" and "I know some rules the US uses", the latter is definitely useful. –  Jefromi Mar 8 at 19:08
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You have two problems here, one easy and one hard. The easy one is "how many servings are in this recipe?" As others have said, the recipe may make 36 cookies but is that 36 servings, or 12, or some other number? That is the easy problem in my opinion. Many recipes say "serves 8" or "serves 6" and you could work out the total numbers for if someone ate the entire batch, then calculate "I can't eat more than 2 of these" or "I should eat at least half of this to get enough protein" as needed.

The harder part is taking raw numbers like how much protein is in an egg or how many calories are in a cup of flour and working out how to combine them. Say you are frying chicken in 1/4 cup of oil. You certainly don't add the oil calories to the chicken calories - not all the oil ends up in the dish. But if you add oil to a cake batter, you will add the oil calories in to the calculation. Some forms of cooking affect some nutrients, so perhaps the Vitamin C in a long cooked fruit dish is not the same as the Vitamin C in the raw fruit you added to it. I don't know a general solution or technique for dealing with this. It depends what nutritional facts you care about (calories? fibre? fat? Vitamin C? B? E?) and how you are cooking the food. In addition if you are using "one apple" or "two carrots" you won't have the same precision as "100g of diced carrot" so your recipe may not be the same every time.

If you just want to know roughly the calories, just add up the calories of the raw ingredients and make some adjustments for ingredients that don't end up in your mouth. Beyond that I don't think it's possible.

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Interesting position. I think that the first part is already hard enough to make it unsolvable. The amount somebody can eat differs with the person. The amount a person predicts she can eat differs with her level of hunger at the moment she is making the prediction. Other external factors such as size of the plate, cookie size, mood during eating and parallel activity will also have a large influence. Basically, people 1) eat different portions of the same food under different circumstances, and 2) are lousy at predicting the average portion (which has too much variance anyway). –  rumtscho Mar 11 at 16:53
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