Calculating the Correct Portion Sizes for Weight Loss

Scooping a portion onto a dinner plate

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Understanding the right portion size for you is necessary for maintaining a healthy weight and a key ingredient to any successful weight-loss program. However, determining the optimal portion size can be challenging. Below, we explore how to calculate the ideal amount of food to put on your plate to achieve your fitness goals.


The simple truth is that weight loss efforts can easily be undermined by large portion sizes. It's easy to end up with more than you realize on your plate.

Irrespective of the type of diet you are on, identifying the correct portion size allows you to know exactly how many calories, carbs, sodium, or fats you're eating. 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

Many of the problems related to portion size stem from misconceptions about what the term actually means. For example, if you use the Nutrition Facts label on a food product to direct your portion size, you may already be significantly off on the calories and other nutrients you are consuming.

What you'll find on the label is the serving size, 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 simply used as a reference point to describe the amount of food in relation to the nutritional information shown.

Portion size, however, 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. If you confuse serving size with portion size, your calorie counts will likely be way off and may undermine your weight loss goals.

Let's say, for example, that you regularly snack on low-calorie 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. Unless you count out the grapes to measure your portion against the serving size, this low-calorie food could quickly increase your carb intake well beyond your intended daily limit.

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.

Calculating Portion Sizes

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.

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 remain at your current weight. However, 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.

To determine your correct portion sizes, use a weight loss calculator to determine how many calories you need to consume daily to lose weight. The calculation is based on your age, sex, height, current weight, activity level, weight loss goal, and intended weight loss date.

Your goal would then be to strategically design menus around those dietary constraints, selecting not only the foods you can eat but how much you can eat. Those are your portion sizes. Oftentimes, it helps to work with a licensed nutritionist when first starting to ensure that the diet plan is safe and meets your daily nutritional goals.

Tips for Portion Control

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

  • Use portion control dishes. To aid in your weight loss goal, invest in a set of portion-control plates, serving spoons, and beverage glasses. They can easily be found online or at larger retail department stores. The dishes often have clever designs that can help guide proper portion sizes.
  • Measure food on a scale. Throughout your diet (but especially at the beginning), it is helpful to use a digital scale to weigh your food accurately. Other measuring methods are available if a scale is not handy.
  • Try smaller plates and bowls. Eating right out of a box or bag can make it nearly impossible to maintain portion sizes if you're not paying attention. Instead, aim to portion out food onto a plate or bowl. Smaller dishes make your food look more substantial.
  • Count your condiments. Don't make the mistake of thinking ketchup or a little extra hummus doesn't matter when it comes to portion size. Measure these out as you would anything else. A heaping tablespoon of peanut butter, for example, may end up being 2 tablespoons, doubling your intake from 95 calories to 190 calories.

A Word From Verywell

There is no question that weight loss requires insight, preparation, and discipline. 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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Article 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. Department of Health and Human Services and U.S. Department of Agriculture. 2020 – 2025 Dietary Guidelines for Americans.

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