How to read a nutrition label and log the right serving size

A nutrition label looks precise, and the numbers on it are about as good as food data gets. Yet most label-based logging errors have nothing to do with the label itself. They come from mixing up columns, trusting the pack's idea of a serving, or logging the dry weight of something you ate cooked.

Here is how to read a label in under a minute and turn it into an entry that matches what you actually ate.

The lines that matter

Labels differ from country to country, but they all answer the same questions. Look for these, in this order:

• Serving size. The amount the manufacturer chose as one serving, often with the number of servings in the pack. It is a convention, not a recommendation, and it is often smaller than a real portion.
• The basis of each column. Many labels show values per 100 g (or 100 ml) and per serving side by side; some show only one. Before you copy a number, check which column it came from.
• Energy. Calories, shown as kcal. Many labels also show kilojoules (kJ); make sure you read the kcal figure, since the kJ number is roughly four times larger.
• Protein, carbohydrate and fat. The three macros. Sugars and saturated fat appear as "of which" lines inside carbohydrate and fat, so do not add them on top.
• Fibre. Handled differently by region: on US-style labels it is included in total carbohydrate, while EU-style labels list it separately. That is why the same food can show different carbohydrate figures in different countries.

A ten-second sanity check

Protein and carbohydrate provide about 4 kcal per gram, fat about 9. Multiply and add, and you should land close to the energy line. If a label says 250 kcal but the macros add up to 400, you are probably mixing the per-serving column with the per-100 g column, or a database entry has a typo.

Fibre, alcohol and rounding mean the figures will rarely match exactly. A gap of a few percent is normal; a gap of half is not.

Weigh the portion, not the pack

The single most useful thing you can do with a label is to ignore its serving size once and weigh what you actually eat. Pour your usual bowl of cereal, your usual spoon of peanut butter, your usual glass of juice, and put each on a kitchen scale. You only need to do it once per food; after that you know your bowl is 60 g rather than the 30 g on the box.

Watch out for dry versus cooked weights. Pasta, rice and oats are labelled dry and gain a lot of weight as they absorb water. If you weigh a cooked portion, log it against a cooked entry, not against the dry label.

Turning a label into an entry in SnapMacro

1. Scan the barcode. Point the camera at the code. If the product is found, the app shows its nutrition before anything is added to your diary.
2. Set the amount in servings or grams. On the confirm screen you can switch between servings and grams, and the serving line shows what one serving weighs. If you weighed your portion, choose grams and type the weight.
3. Pick the meal and check the total. Choose breakfast, lunch, dinner or snack, and look at the total for the entry before you log it.
4. If the barcode is not found, add the product yourself. The app offers to add it manually: enter the name, optionally the brand, a serving size in grams, and the calories, protein, carbohydrate and fat for that serving.
5. Use the per 100 g column for a flexible entry. Set the serving size to 100 g and copy the per 100 g figures. Later you can log any weight in grams without doing the arithmetic yourself.
6. Reuse it. Foods you create show up in search afterwards, and anything you have logged appears under Recent foods for quick re-logging.

Limits worth knowing

Label values are rounded and allowed some tolerance, and product databases can lag behind when a recipe changes. If a scanned entry looks wrong next to the pack in your hand, trust the pack and create your own entry from it.

Nutrition figures are estimates for tracking, not medical measurements. If you are managing a medical condition, a food allergy or a prescribed diet, a doctor or registered dietitian is the right person to advise you.

Barcode, search and manual entries do not count towards the AI photo-analysis limit. Photo logging includes a limited number of free analyses; unlimited photo logging comes with SnapMacro Premium, and the app shows what your plan includes.