The serving size of a food product is a confusing term, as it is found both on the Food Pyramid and on Nutrition Labels and has two related but differing meanings. The USDA Center for Nutrition Policy and Promotion sets the standards for these meanings in the United States.

Food Pyramid

The purpose of The Food Pyramid is to assist people in meeting daily nutrient recommendations while providing relatively few serving sizes for each food group.

According to the USDA, serving sizes in the Pyramid are determined through four factors:

1. The considering of typical portion sizes from food consumption surveys.
2. Convenience in relation to common measuring sizes.
3. Nutrient content.
4. Sizes from previous guides.

Some food groups receive different emphasis than others. See Food Pyramid for recommended daily servings.

Nutrition Facts Label

Nutrition Facts Label Serving Sizes are specific in their nutritional information to allow for easy comparison with other similar foods. Consumers may visualize important nutritional variations without excessive calculation. While designed for easy comparison with other similar products, such as Coke vs. Diet Coke or Fruit Loops vs. Frosted Flakes, the label is not meant for direct comparison with the Food Pyramid's recommended servings.

Serving sizes on Nutrition Facts Labels are loosely based on the amount of a product normally eaten in one sitting or reference amounts, determined from nationwide food consumption surveys. The variation in caloric content per serving from product to product is normally because of the reference amount, not because of any set value or common unit.

Reference amounts affect serving sizes in one of three ways:

1. Bulk products, such as sugar, have sizes in common units of measurement, such as the cup or tablespoon, to show the quantity closest to the reference amount.
2. Commonly divided products, such as pie or cake, have a serving size given in a fraction of the whole product (e.g., 1/8 pizza).
3. Products which are sliced beforehand or are bought in distinct, grouped units (such as olives), are listed in the approximate number of units corresponding to the reference amount. For example, if the reference amount for olives were 30 g, and one olive weighed 10 g, the serving size would probably be listed as three olives.

One serving of grain: one cup of whole grain cereal, one fourth of a bagel, one cup of pasta.
One serving of vegetables: five cherry tomatoes, five sticks of celery, one whole carrot.
One serving of fruit: Half of an apple, fifteen large grapes, half a banana.
One serving of dairy: Half cup of milk, three cheese cubes, half cup of low fat cottage cheese.
One serving of meat: 1/4 chicken breast, daily guide line: one fist full per meal.
Fats and Sugars: as little as possible, dairy and meat contain plenty of necessary fat, while fruits contain enough natural sugars.