Serving Size vs. Portion Size: What’s the Difference?

The terms serving size and portion size are often used interchangeably, however, they are not the same thing, and understanding the difference between them can help to bring some clarity to your food choices. Here’s a breakdown of the definition of serving size and portion size, the differences between them, as well as an explanation of how to determine portion sizes and how to convert serving sizes to portion sizes.

What’s the difference between serving size and portion size?

A serving size is the amount of food listed on a packaged food’s nutrition facts label, while a portion size is how much food you choose to eat at one time.

Serving sizes are standardized measurements; listed in common household measurements such as cups or tablespoons, followed by the metric amount in grams, and are used to quantify nutrition data for comparative purposes. (1)(2) The serving size tells you the quantity of food used to calculate the numbers in the nutrition facts table and are not necessarily the suggested quantity of food you should eat.

By checking the serving size on a label you can understand how many servings a package of food contains, how much food is required to consume the listed calories and nutrients, and compare nutrition information on different products.

A portion size is how much an individual chooses to eat at one time, which may be more or less than a serving size. Although some health organizations, including the FDA, have changed serving sizes to more closely reflect the amount of food people typically eat, it does not always match.

For instance, if the serving size on a package of ice cream is a 1/2 cup but an individual chooses to eat 1 cup of ice cream, although they are eating one portion of ice cream they are in fact consuming 2 servings.

Remember, the serving size on a label is not a recommendation for how much you should eat; it is a standardized measurement to be used for data and comparative purposes.

How to Determine a Portion Size

There are many different ways to determine exactly how much you should eat, from calorie counting to macro counting, however, a simple and effective way to estimate portion sizes is to use your hand. (3) Using your hand as a tool can help you estimate portion sizes for different foods and manage your total calorie intake to help ensure you aren’t eating too little or too much. Your hand is a great portioning tool because it is proportionate to your body, its size never changes, it’s always with you, and there is no weighing or measuring required. The hand portion method can be used for different foods as follows:

• 1 portion of protein = 1 palm
• 1 portion of carbohydrates = 1 fist
• 1 portion of fruits and vegetables = 1 fist
• 1 portion of fat = 1 thumb

Estimating Portion Sizes with Your Hand

Converting Serving Sizes into Portion Sizes

Once you’ve determined your portion size, you can use the information from the serving size on the nutrient facts label to determine the nutritional value of your portion size. By doing a little math you can determine exactly how many calories and how much fat, carbohydrate, fiber, and protein you are consuming in your chosen portion.

For example, if the serving size of a cracker brand is 4 crackers according to the nutrition facts labels and includes 70 calories, 3 grams of fat, 10 grams of carbohydrate, 1 gram of fiber, and 1 gram of protein, but an individual chooses to eat 12 crackers, which is 3 times the serving size, the nutrition information of the portion size can be determined by multiplying by 3. Therefore, the nutritional value of their portion size would be 210 calories, 9 grams of fat, 30 grams of carbohydrate, 3 grams of fiber, and 3 grams of protein.

All nutrition data from USDA multigrain crackers.

The Bottom Line

Serving sizes and portion sizes are not the same. A serving size is a standardized measurement found on a product’s nutrition facts labels, while a portion size is the amount of food an individual chooses to eat. Serving sizes are not designed as recommended portion sizes but rather for comparative purposes or to determine the nutrition information of the portion size consumed.