QUOTE

The Food and Drug Administration provides an exhaustively detailed set of guidelines* to help manufacturers set portion size based on the amount the average person is likely to eat at once—or, in jargon, the "reference amount customarily consumed." The agency arrives at this figure—always expressed in grams—by factoring in survey data, recommendations from food and nutrition organizations, and customs in other countries. One reason official serving sizes seem so small is that the survey data comes largely from studies conducted by the U.S. Department of Agriculture in the 1970s and '80s, when Americans consumed less food than they do now.

UNQUOTE

http://www.slate.com/articles/news_and_politics/explainer/2010/01/this_pint_of_ben_jerrys_is_four_servings.html

*http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=101.12

Package size is determined by

1. whether the product is likely to be shopped for on a daily, weekly or monthly basis (milk, bananas or cornflakes);

2. how many people are in the family being shopped for;

3. how many times a day on average the family are expected consume that food;

4. how visible it will be on the supermarket shelf;

5. what is a convenient size to manufacture, containerize, ship, display and store. If it is too bulky, it might take up too much space in the pantry or expire too quickly; If it is packaged too small, it might be overlooked by the shopper or result in more shoplifting.