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What is the difference between portion and serving size?

The terms portion and serving size seem to be thrown around and used interchangeably but subtle differences exist.
16th Apr 2021

In navigating Nutritics, a user will likely encounter both the term portion, and serving size. Deciphering between the two metrics can be difficult - this article will help users to make the distinction. A portion can be defined as the quantity of food eaten at any one time/sitting, e.g a meal or snack (1). Portion sizes vary from person to person and are at the discretion of the individual. In contrast, serving sizes are standard quantities of food served e.g. a serving on the Nutrition Facts Label of a product. To illustrate, a portion, or meal can contain multiple servings (2).

Portion Size

Nutrition requirements vary from person to person, and for this reason it is difficult to estimate portion sizes for each meal. The British Nutrition Foundation suggests these practical measurements to approximate the portion size (3):

  • 2 handfuls of dried pasta shapes or rice (75g);
  • A bunch of spaghetti the size of a coin measured using your finger and thumb (75g);
  • the amount of cooked pasta or rice that would fit in two hands cupped together (180g);
  • A baked potato about the size of your fist (220g);
  • About 3 handfuls of breakfast cereal (40g);
  • A piece of grilled chicken breast about half the size of your hand (120g);
  • A piece of cheddar cheese about the size of two thumbs together (30g);
  • About 1 tablespoon of peanut butter (20g);
  • About 3 teaspoons of soft cheese (30g);

For further information please access:

Visual Cues of Portion Sizes

Visual cues play a considerable role in determining portion size and perception and have the power to prevent/exacerbate overeating. A study, consisting of 54 participants aged 18 to 46 years old, examined whether visual cues relating to portion size can influence intake volume without altering either estimated intake or satiation, using self-refilling soup bowls. Participants that were unknowingly eating from self-refilling bowls ate more soup than those eating from normal soup bowls. Even though they consumed 73% more, they did not believe they had consumed more, nor did they perceive themselves as more satiated than those eating from normal bowls (4).

Portion size & Food intake

Further research examined the effect that exposure to smaller portion sizes has on future portion size selection. (5) The study tested “whether reducing a food portion size “renormalized” perceptions of what constitutes a normal amount of that food to eat and results in people selecting and consuming smaller portions of that food in the future”(5). Across 3 experiments, participants were served a larger or smaller portion of food. In experiments 1 and 2, participants selected and consumed a portion of that food 24 hours later. In experiment 3, participants reported on their preferred ideal portion size of that food after 1 week. The consumption of a smaller portion size resulted in participants believing a “normal”-sized portion was smaller. Therefore, reducing food portion sizes can recalibrate consumer’s perception of a ‘normal’ portion size, and as a result, encourage overconsumption (5).

Barriers that Affect Portion Size Control

Barriers affecting portion size control are another area of key interest in the literature. A recent study included 66 individuals living on the island of Ireland and identified seven key barriers to appropriate portion size control:” lack of clarity and irrelevance of suggested serving size guidance; guiltless eating; lack of self-control over food cues; distracted eating; social pressures; emotional eating rewards; and quantification habits ingrained from childhood” (6). Participants attributed their lack of portion size control to quantitative habits ingrained from childhood, social pressures and emotions (6). Serving size guidance needs to resonate with consumers and be seen as relevant to their eating behaviour. Interventions should raise awareness of ‘portion size distortion’, correct misconceptions regarding food nutritional properties, and, raise awareness of behaviour priming effects, while at the same time advising on the various options to overcome unwanted influences (6).

Serving Size

A serving is a measured amount of food or drink, such as one slice of bread or one cup (eight ounces) of milk. A nutrition facts label shows nutritional information for the serving size recommended by the manufacturer.

The infographic below shows the recommended serving size by HSE Ireland.

Displayed below is US national guidance for nutritional needs based on the the United States Department of Agriculture guidance (7):

Portion sizes differ throughout the world according to culture and availability of different foods.

For more information and resources access:

Serving size and Food Intake

The serving size on the manufacturer’s label is likely to influence consumption of discretionary foods. “The impact appears to depend on whether total energy per serving or the number of servings contained is emphasised” (8).

Three studies that took place in the US looked at behavioural outcomes of increasing serving sizes included on food labels. Results showed that participants presented with the larger serving size label consumed less than those presented with the current serving size label. Together, the results suggest that the proposed increase in serving sizes on Nutrition Facts Panels could lower consumption of high-calorie foods (9).

Nutritics Smart Portions

Nutritics offers a smart portion feature that allows users to choose between different serving sizes for both foods and recipes. Portion sizes are provided for a large number of foods in the database. These are assigned to foods from various portion size resources, manufacturer’s data or from direct weighing by trained Nutritics staff. Serving sizes have visual aids, calorie measurement and full micro- and macronutrient breakdown, as shown in the image below. Clients can also set their own servings when creating a recipe or adding a food. For more information on the use of Nutritics smart potions, please visit this link.

portion size, serving size, nutritics


  1. National heart, lung and blood institute, N.H.L.B.I. Serving Sizes and Portions. [Online]. Available from: ;
  2. American heart association, A.H.A. Portion Size Versus Serving Size. Nutrition Basics. Weblog. [Online] Available from:
  3. British nutrition foundation. Find your balance - get portion wise!. [Online]. Available from:;
  4. Wansink B, Painter JE, North J. Bottomless bowls: why visual cues of portion size may influence intake. Obes Res. 2005 Jan;13(1):93-100. doi:;
  5. Eric Robinson, Inge Kersbergen, Portion size and later food intake: evidence on the “normalizing” effect of reducing food portion sizes, The American Journal of Clinical Nutrition, Volume 107, Issue 4, April 2018, Pages 640–646,;
  6. Spence, M., Livingstone, M.B.E., Hollywood, L.E. et al. A qualitative study of psychological, social and behavioral barriers to appropriate food portion size control. Int J Behav Nutr Phys Act 10, 92 (2013).;
  7. Kelly Magowan, A Dietitian’s Guide to Portions and Serving Sizes, feedyourpotential365 [Online] Available from:;
  8. Tamara Bucher, Beatrice Murawski, Kerith Duncanson, David Labbe, Klazine Van der Horst,The effect of the labelled serving size on consumption: A systematic review, Appetite,Volume 128,2018,Pages 50-57,ISSN 0195-6663,;
  9. Chris Hydock, Anne Wilson, Karthik Easwar,The effects of increased serving sizes on consumption,Appetite,Volume 101,2016,Pages 71-79,ISSN 0195-6663,;