Measuring and Estimating Portion Size

  • 6 Minutes Read
  • May 14, 2018

The real challenge to recording food intake is figuring out how much food or drink was actually consumed.

Measuring and Estimating Portion Size

One of the main sources of error in a food log is inaccurate portion size. When we don’t measure our portions, we almost always underestimate how much we really eat. This is why so many of us struggle with weight loss, even if we are tracking calories. Measuring is much more accurate than guessing. The more frequently you measure, the better you will be at guessing portion size when measuring is not possible. This is especially helpful when you go to parties, dine out, or when you travel.

Weigh Your Foods If Possible

Weighing is typically the most accurate way to measure portion size. Food labels use weight for nutrient content, even if a volume measurement is provided. For example, breakfast cereals list the serving size in cups but they also include the weight of that serving size.

Use a digital kitchen scale to weigh foods - this will be more accurate, faster, and easier to use than an old-fashioned spring-loaded scale. 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.). Digital scales can be bought online or from local stores that sell kitchen and cooking related products. There are many affordable brands available.

Measuring Cups & Spoons

Sometimes we don’t have a choice in how we measure food items. For instance, the serving size on a food label for oils and beverages might be listed as a volume (e.g. cups, fl oz, ml, etc.) without a weight. In that case, you need to know how to measure volume.

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

When measuring a liquid, it is easier, more accurate, and less messy if you use a measuring cup designed for liquids. 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.

For measuring very small amounts of liquids or solids, you can use measuring spoons. 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.

Always Measure Calorie-Dense Foods

Some foods are so high in calories that an error in portion size means a large error in calories intake. Therefore, I strongly recommend that you always measure the following items:

Always Measure Comfort & Snack Foods

Let’s be honest. If you consume foods straight out of the original packaging, then you have no idea how much you have eaten unless you eat the entire package. Just say “no” to this behavior. Portion out what you want, log it, and then enjoy it. I have saved myself hundreds of calories by implementing this simple rule.

I have made a list of foods that I tend to overeat unless I carefully portion control ahead of time.

Make up your own list of items and post somewhere near the food - on the fridge or maybe on the kitchen counter.

Tricky Portion Sizes

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

Tip: add “raw” to your name search to find basic fresh fruit or vegetables.

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

Estimating Portion Size

If you have already started recording your intake, then you know how difficult it is to estimate portion size. For restaurant chains, the nutrition information should be posted on their website. For other restaurants, you might have to guess if your server does not know the portion size.

For more help on 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’s How to Estimate Portion Size 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 of 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.

Ask Us for Help

If you need help figuring out how to log a food item, or just have questions about nutrition, weight, or diabetes, post us a question at “Ask a Registered Dietitian” forum in Community. We would love to help you.

Katherine Isacks
Katherine Isacks, MPS, RDN, CDE - Registered Dietitian and Certified Diabetes Educator (CDE)

Last Updated on May 14, 2018

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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