The difference between a portion and 100 grams
If one packet of crisps shows 90 calories and another 250, the difference may lie not in the product but in the basis of the calculation: one is written per portion and the other per 100 grams. That small detail is the source of the most common misreading of labels.
Short answer
On labels, the 100 gram figure is a standard basis for comparison, while the portion figure is calculated from an amount the manufacturer has chosen, and that amount may be smaller than what you actually eat. Always use the 100 gram column when comparing products, and use your own realistic portion when thinking about what you have taken.
Two columns, two different questions
The two presentations in a nutrition table actually answer two separate questions. The 100 gram figure answers “how dense is this product?”, and because the same basis is used for every product it is the only reliable way of comparing them. The portion figure answers “what do I get if I eat the stated amount?” Mixing the two ends in taking a dense product for a light one, or a light product for a dense one.
Who decides the portion?
The portion size on a label is set by the manufacturer, and that choice does not always reflect how people eat. The label of a 150 gram packet of crisps may be written on the basis of a 25 gram portion, so someone who finishes the packet in one sitting has taken six times the figure on the label. Choosing a small portion also makes the numbers on the front look small; that is legal but can be misleading. Whenever you see a portion figure, then, the first question should be: “How many grams is this portion, and how much am I really eating?”
Always compare on a 100 gram basis
Think of two brands of granola: one says 120 kcal per portion (a 30 g portion), the other 180 kcal per portion (a 45 g portion). At first glance the first looks lighter; converted to a 100 gram basis, however, both are around 400 kcal. As long as portion sizes differ, portion figures cannot be compared. The same rule applies to comparisons of sugar, salt and fat. For the habit of reading a label as a whole, see the food label guide.
A realistic portion: your own measure
When you think about your own consumption, what counts is your real portion, not the label portion. You can calibrate this by weighing once or twice: weighing the slice of cheese you eat every day, the cereal you pour or your spoonful of olive oil just once makes your later estimates by eye considerably more accurate. Research shows that estimates by eye generally fall short of reality, and a one-off weighing habit narrows that gap. Liquids and oils are the items people misjudge most.
Hand measures: a practical estimate without scales
Where there are no scales, whether eating out, visiting or at work, your own hand can become a portable measuring tool; because hand size is roughly proportional to body size, the method offers a personalised estimate. The commonly used equivalents are these: one palm, excluding the fingers, is about a portion of meat, chicken or fish; one fist is about a portion of rice, pasta or fruit; one thumb is about a tablespoon of oil, peanut butter or cheese; and the bowl formed by two hands is about a portion of salad or greens. These measures do not offer gram-level precision, nor do they need to. Their job is to reduce the large deviations that come from looking at a plate and estimating with no reference at all. A hand measure checked against scales a few times at home noticeably improves the accuracy of your estimates elsewhere, and it is the least demanding way to keep portion awareness going without counting.
Common traps
- Small portions that look light: a low calorie claim on a pack is often the result of choosing a small portion.
- Assuming the pack is one portion: many packs that look single-serving are defined on the label as two or three portions.
- Prepared and unprepared states: in some products the figures refer to the state before milk is added or before cooking.
- Percentage reference values: expressions such as “percentage of daily requirement” are based on a general reference of 2000 kcal, and your own need may differ. The TDEE guide gives an idea of your own estimated range.
The antidote to all these traps is the same: when you see a number, ask what it is based on. “What is this figure for: a portion of how many grams, 100 grams, or the prepared state?” is the shortest and most protective reflex in label reading.
Frequently asked questions
Why do labels not simply use 100 grams?
Regulation makes the 100 gram (or 100 ml) figure compulsory, while the portion figure is additional information. Showing a portion can be useful; the problem is using portion figures for comparison by mistake.
Does the same logic apply to liquids?
Yes; for liquids the basis is 100 ml. Someone drinking from a litre bottle with a large glass takes several times the 100 ml figure, and the rule is the same.
Do I need scales to measure portions?
Constant weighing is not necessary. Weighing the foods you eat often once and matching them to your own vessels, such as a glass or a tablespoon, gives enough accuracy for everyday use.
How can I judge restaurant portions?
Restaurant portions are usually larger than label portions and are not standardised. Using your home portions as a reference for a rough comparison, and remembering that an estimate is an estimate, is the most realistic approach.
This guide draws on the principle of presenting values per 100 grams or 100 millilitres in the labelling rules of the Turkish Food Codex, the national food regulation in Türkiye, and on the general findings of nutrition research into portion perception.