Turn a packet over and you will usually find a small table with a column "per 100 g" and sometimes another "per portion". They look similar, but they answer different questions. The per 100 g column is the same on every product, so it is the fair way to compare two cereals or two soups. The per portion column is the manufacturer's idea of how much you will eat, and it may be smaller or larger than what ends up in your bowl. In the EU and the UK the per 100 g (or per 100 ml) figures are required; the per portion ones are optional.
The trick is to use both: compare products on 100 g, then work out what your serving contains. The reader below does that sum for you. Type in the numbers from any label (or tap an example), then change how many grams you actually eat.
| Per 100 g | Serving | Daily ref.* | Rating |
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Energy is shown in kilojoules (kJ) and kilocalories (kcal). One kcal is about 4.2 kJ, so a label that says 1,880 kJ means roughly 450 kcal. Fat, carbohydrate and protein are where the energy comes from. EU labelling rules use these conversion factors: about 9 kcal per gram of fat, 4 per gram of carbohydrate and protein, 2 per gram of fibre and 7 per gram of alcohol. That is why the reader can cross-check the energy line against the other numbers.
"Of which sugars" is part of the carbohydrate line, not an extra. It includes sugar naturally present in milk and fruit as well as sugar added to the food, so a plain yoghurt shows some sugars even with none added. For added ("free") sugars, the WHO advises keeping them under 10% of daily energy, with further benefit below 5%. Salt is sometimes shown as sodium; multiply sodium by 2.5 to get salt. The WHO suggests adults stay under 5 g of salt a day.
Compare foods on 100 g; judge your own plate on the portion you actually eat.
The NHS gives simple guide values per 100 g. Fat is high above 17.5 g and low at 3 g or less. Saturates are high above 5 g and low at 1.5 g or less. Sugars are high above 22.5 g and low at 5 g or less. Salt is high above 1.5 g and low at 0.3 g or less. Anything in between is medium. The reader uses these to tag each line. They are for comparing everyday foods, not a verdict on one item: a small amount of olive oil, cheese or granola can sit happily in a balanced week, and the tag says nothing about fibre, protein or how filling a food is.
Watch the portion trap too. A cereal label may show "30 g" as a portion, while a typical bowl is often more than that. Try 30 g and then 60 g in the reader to see how the numbers move. Labels also round, and the figures can be off by a margin, so treat small differences between two products as a tie.
You do not need to weigh food forever. A few weeks of weighing the foods you eat most, such as cereal, rice, pasta, oil and cheese, teaches your eye what a portion looks like, and then you can stop. If you want to try it, a scale is the one piece of kit that makes label numbers real. Whatever you spend, these matter most:
Numbers on a packet help you notice what you eat; they do not say how you should eat. If you have a medical condition such as diabetes or high blood pressure, are pregnant or breastfeeding, take medication, or have or have had an eating disorder, please talk to a doctor or dietitian before changing how you eat. Counting every gram can also feel stressful for some people; if it starts to, put the scale away. This guide is general information, not medical advice.