Calculating Portion Sizes for Weight Loss

Scooping a portion onto a dinner plate

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If you have a weight loss goal, considering portion control in your diet may be helpful. However, determining the optimal portion size can be challenging. Below, we explore how to become more mindful of portion sizes to help you reach your fitness goals.

What Is Portion Control?

Portion control is the act of being aware of the actual amount of food you eat and adjusting it based on its nutritional value and the goals of your eating plan. The simple truth is large or unbalanced portion sizes can easily undermine that weight loss efforts. It's easy to end up with more than you realize on your plate.

Portion control can help you create a nutrient-dense eating pattern. By honing in on how food makes you feel, you can learn how to adjust your portion sizes of those foods accordingly. This knowledge is the cornerstone of building good eating habits, which will increase your chances of achieving your health goals.

Portion Size vs. Serving Size

There's a lot of confusion about the difference between serving size and portion size. Put simply, serving size is what's on the label, whereas portion size is what's on your plate.

You'll find the serving size for that food on the Nutrition Facts label on most packaged foods. Some people misconstrue the serving size for the amount they're supposed to eat, but that's not the case.

Serving size is a standard set by the Food and Drug Administration (FDA) to describe "the amount of food customarily consumed in one sitting for that food." It is used as a reference point to define the amount of food in relation to the nutritional information shown.

Portion size, on the other hand, is the amount of a specific food that you actually eat. It is often larger or smaller than the serving size on the nutrition label.

Let's say, for example, that you regularly snack on microwave popcorn. A serving size according to the Nutrition Facts label is 3 cups. There are two servings in each full-size bag. If you eat the whole bag, your portion size is 6 cups—double the serving size and double the nutrition values.

Similarly, the recommended serving size of grapes is 1 cup or roughly 16 grapes. If you eat more or less than that, you're consuming a different amount of nutrients than what is listed on the nutrition label for the 1-cup serving size.

This is true even with respect to certain diet apps that base their calculations on FDA serving sizes. Unless you have the reference values and make the appropriate adjustments—such as inputting eight grapes as a half-portion or 20 grapes as a 1.25-portion—the app will be of little benefit to your weight loss strategy.

How to Calculate Portion Size

There is no right or wrong amount of specific food to eat when you want to lose weight. The proper portion sizes of food are the portions that allow you to fuel your body with energy and nutrients and feel satisfied.

If your weight loss plan includes tracking calories, you can use your total daily calorie goal to help determine corresponding portion sizes.

Unlike serving size, the portion size should be calculated based on how many calories you plan to consume in a day. You would then plan your menus by calculating how much of a certain food you can eat to remain within that limit.

The ultimate aim of any weight loss plan is to consume fewer calories than your body utilizes. To accomplish this goal sustainably and healthfully, you need to do so without depriving yourself of important nutrients, including healthy fats and carbohydrates.

As such, portion sizes can vary as long as nutritional needs are met. These goals are outlined in the 2020-2025 USDA Dietary Guidelines issued by the U.S. Department of Health and Human Services and the U.S. Department of Agriculture.

A calorie goal calculator can help you set a daily calorie goal. The calculation is based on your age, sex, height, current weight, activity level, and weight loss goal.

Practical Portion Control

Experiment with portion sizes that help you plan meals that are satisfying but also allow you to work toward your goals. It's not always an exact science and may require a lot of trial and error.

You may find that a portion of food (let's say 3 ounces of chicken, for example) may fill you up one day and leave you hungry the next. Working with a registered dietitian when first starting out might be helpful to ensure that your diet plan is safe and meets your daily nutritional goals.

Once you know how much to eat, you may need to take extra steps to ensure the portion sizes are accurate.

  • Try the plate method. Use these guidelines to fill a plate at meals as a simple way to control portions without weighing or measuring food:
  1. Fill half the plate with vegetables, whether they are cooked or tossed in a salad.
  2. Fill a quarter of the plate with lean protein such as meat, seafood, poultry, eggs, dairy, legumes, tofu.
  3. Fill the remaining quarter of the plate with complex carbohydrates, such as whole grains.
  • Use portion control dishes. To aid in your weight loss goal, you may choose to invest in a set of portion-control plates, serving spoons, and beverage glasses. The dishes often have clever designs that can help guide proper portion sizes. Looking for an alternative option? Smaller dishes work too; they make your food look more substantial and can influence how much you serve yourself.
  • Measure food on a scale. A digital scale can be useful to help you understand portion sizes, especially when you first start a weight loss plan. Other measuring methods are available if a scale is not handy.
  • Practice mindful eating. The next time you find yourself mindlessly snacking on energy-dense foods, question why you're eating and whether you're really hungry. Portion out food onto a plate or bowl rather than eating right out of a box or bag.

A Word From Verywell

Portion control can be a powerful method for eating more nutrient-dense foods and fueling your body while you work towards your weight loss goals. Simply being aware of the portion sizes you're eating is often the first step to making a change if you are working toward a weight loss goal. By establishing good habits from the start, you are more likely to reach your fitness goals and develop healthy eating habits without unneeded stress or anxiety.

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4 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Rolls BJ. What is the role of portion control in weight management?. Int J Obes. 2014;38 Suppl 1:S1-S8. doi:10.1038/ijo.2014.82

  2. U.S. Food & Drug Administration. CFR- Code of Federal Regulations Title 21. Updated April 1, 2020.

  3. U.S. Department of Health and Human Services and U.S. Department of Agriculture. 2020 – 2025 Dietary Guidelines for Americans.

  4. Sharp DR, Sobal J, Wansink B. Using plate mapping to examine portion size and plate composition for large and small divided platesEating Behaviors. 2014;15(4):658-663. doi:10.1016/j.eatbeh.2014.08.022

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