Understanding how to calculate portion size

  • 15 Minutes Read
Katherine Isacks Katherine Isacks, MPS, RDN - Registered Dietitian

Sue Heikkinen Joanna Kriehn, MS, RDN, CDCES - Registered Dietitian and Certified Diabetes Care and Certified Diabetes Care and Education Specialist (CDCES)

If you are new to logging or have been at it for a while, you may have wondered about the best way to measure or calculate portion size. A key aspect of tracking is accurately determining how much food and drink you’ve consumed.

How to calculate portion size

If you don't measure your portions, you’ll often underestimate how much you are taking in. If you are trying to lose weight, this can lead to frustration and a lack of progress. Figuring out portions of commonly consumed foods, such as bread or crackers, where the serving size is listed on the package, is straightforward. However, what about figuring out portions of pasta, meat, peanut butter, and oils?

This article delves into the details of calculating the portion size of foods and drinks, with specifics around weighing, measuring, and estimating food portions for weight loss.

How to calculate portions with accuracy Weigh your food!

Weighing is the most accurate way to measure or calculate portion size. You can purchase a kitchen scale at most big box stores or online. We suggest investing in a digital scale as opposed to an old-fashioned spring-loaded scale. The digital scales are easier to use and more accurate. With a digital scale, you can easily zero out the weight of the container as well as select different units of measure (e.g. grams, ounces, etc.). Serious about losing weight? Check out MyNetDiary and start weighing your food!

Measuring volume- Use measuring cups & spoons

Another approach to calculating portion size is to use measuring cups and spoons or a glass measuring cup to determine volume (e.g., cups, fl oz, ml, etc.). These items can be purchased at big box stores or online.

Using a measuring cup designed for liquids is easier, more accurate, and less messy. See below for an example of this type of measuring cup.

When measuring the volume of a solid (e.g. flour, cereal, etc.), you can use standard measuring cups (if measuring weight is not an option). Level off the contents with the flat side of a knife to get an accurate measurement. Use metal or plastic measuring cups, whichever you prefer. Standard measuring cups look like those shown in the photo below.

You can use measuring spoons to measure very small amounts of liquids or solids. Level off solids with the flat side of a knife. Use metal or plastic measuring spoons—whichever you prefer. They look like the ones shown in the photo below.

Buy several sets of measuring cups and spoons. That way, you always have one clean and ready for measuring.

Estimating portion size

If you have already started recording your intake, then you know how difficult it is to estimate portion size. MyNetDiary created a Portion Guide to aid in the process. Look for the open book icon (see example below) when tracking to access the guide.

Tip: Metric system is available for weight, length, and volume measurements.

For more help estimating portion size when you cannot measure, check out the Serving Size Card from the National Heart, Lung, and Blood Institute. This card displays portion size using familiar objects. Also, visit WikiHow for more helpful visual representations of portion size. See below for a quick summary.

Grain Products 1 cup cereal flakes = 1 fist
1/2 cup cooked rice, pasta or potato = 1 tennis ball
1 oz slice of bread = 1 cassette tape
1 oz chips = 1 handful
Vegetables, and Fruit 1 cup salad greens = 1 baseball
1 medium baked potato = 1 computer mouse
1 medium piece fruit = 1 baseball
1/2 cup fresh fruit = 1 tennis ball
1/4 cup raisins = 1 egg
Dairy and Cheese 1½ oz cheese = 4 stacked dice
1/2 cup ice cream = 1 tennis ball
Meat and Protein Alternatives 3 oz meat, fish, or poultry = 1 deck of cards
3 oz fish fillet = 1 checkbook
2 tablespoons peanut butter = 1 ping pong ball
Fats 1 teaspoon = 1 dice or tip of a finger
1 tablespoon = 1 poker chip

Tip: We tend to serve ourselves more food when we use larger dishes and less food when we use smaller dishes. If you are trying to lose weight, consider using smaller plates and bowls if you are not able to measure your portion size.

Always measure calorie-dense foods

Some foods are so high in calories that an error in portion size means a large error in calorie intake. If you are focusing on selecting portions for weight loss, this can translate to unexpected calorie intake and potentially impact your weight loss.

Consider always measuring the following items:

Always measure comfort & snack foods

Let’s be honest. If you consume foods straight out of the original packaging, you have no idea how much you have eaten unless you eat the entire package. Portion out what you want, log it, and then enjoy it. By implementing this simple rule, you can save hundreds of calories.

Here is a list of foods people tend to overeat unless portioning out ahead of time:

Make up your own list of items and post somewhere near the food - This will help remind you to measure out these items before eating them!

Tricky portion sizes

Food labels typically display serving size as consumed, but not always. There are many exceptions that make logging a bit tricky. Here are some tips that will help you calculate portion size.

Measurement equivalents

The measurements provided in the table below might be helpful when logging.

English Metric
1 teaspoon = 0.33 tablespoon 5 ml
3 teaspoons = 1 tablespoon 15 ml
2 tablespoons = 1 fl oz = 1/8 cup = 0.125 cup 30 ml
4 tablespoons = 2 fl oz = 1/4 cup = 0.25 cup 60 ml
6 tablespoons = 3 fl oz = 0.38 cup 90 ml
8 tablespoons = 4 fl oz = 1/2 cup = 0.5 cup 120 ml
16 tablespoons = 8 fl oz = 1 cup 240 ml
16 fl oz = 2 cups = 1 pint = 0.5 quart 480 ml
32 fl oz = 4 cups = 2 pints = 1 quart 960 ml (just less than 1 Liter or 1000 ml)
1 oz 28 grams
3 oz 85 grams
3.5 oz 100 grams

Ask us for help

If you need help logging a food item or just have questions about nutrition, weight, or diabetes, post them at the “Ask RD” forum in the Community. We are available to help.

Still new to MyNetDiary? Learn more today by downloading the app for FREE.

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Last Updated on Jan 30, 2020

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Disclaimer: The information provided here does not constitute medical advice. If you are seeking medical advice, please visit your healthcare provider or medical professional.

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