How to read a food label and calculate your serving calories

Read the amount attached to the nutrition column

Before copying a calorie value, find what it describes: 100 g, 100 ml, one serving, or the whole package. Then compare that basis with the amount you actually consumed. A package can contain several servings, and the largest printed calorie number is not necessarily the one that matches your portion.

The NHS explains that UK nutrition information is provided per 100 g or 100 ml and sometimes per portion. The FDA explains that a US label's serving size reflects typical consumption, rather than a recommended amount to eat. These are label reference amounts; your diary should describe the amount you consumed.

Sources: [1], [2]

Convert values per 100 g to your weighed portion

Use this calculation: listed value multiplied by consumed grams divided by 100. Suppose a hypothetical product lists 240 kcal, 8 g protein, 30 g carbohydrate and 10 g fat per 100 g. If you weigh 75 g of that product, the multiplier is 0.75.

Your entry is therefore 180 kcal, 6 g protein, 22.5 g carbohydrate and 7.5 g fat. Those figures come from the label and your measured amount. A food photo did not measure them. If you instead estimate that the portion is about 75 g, the arithmetic stays the same but uncertainty in the amount remains.

Do the calculation once, using a single consistent multiplier. Copying the calorie total for 75 g while leaving the macros at their per-100 g values creates an entry whose fields describe different portions.

Convert a labelled serving or package fraction

For values per serving, divide your consumed amount by the labelled serving amount. A hypothetical snack lists 160 kcal per 40 g serving. Eating 60 g means 1.5 servings and 240 kcal. Multiply each listed macro by 1.5 as well. Do not assume the whole bag is one serving just because you ate it at once.

When a pack has two equal servings and you eat the whole pack, double the per-serving values. If it also gives a per-package column, use that matching column directly. Avoid adding the per-serving and per-package figures together: they are two descriptions of the same product, not separate foods.

Sources: [2]

Check whether the label describes the food as sold or prepared

Read the wording around the nutrition table, especially for powders, concentrates and foods with preparation instructions. If the figures describe the product prepared with a stated amount of milk, check whether your preparation matches. Do not add that same milk again if it is already included in the nutrition basis you use.

If your preparation differs, use the product information that matches what you can establish and calculate additions separately. Keep uncooked ingredient weights separate from the weight of a finished dish. A cooking instruction does not automatically tell you which state every nutrition column describes, so check the specific package rather than assuming.

Keep calories, kilojoules and macros in the right fields

UK labels show energy in both kJ and kcal. For a field asking for calories in kcal, copy the kcal value. Do not add both energy numbers or enter the kJ figure as calories. They express energy in different units. Check the nutrient units too, since grams and milligrams are different quantities.

Use the total carbohydrate line for carbohydrates, rather than the sugars line. Sugars are included within total carbohydrate on the FDA label, so adding them again would duplicate part of the total. Copy protein and fat from the same column and scale every field to the same consumed amount.

Sources: [1], [3]

Enter a complete portion in CalQuest

Use manual entry for your calculated numbers and a food name that identifies the product. Make the amount clear, for example yoghurt, 150 g, or snack, whole 60 g pack. Review the final serving description, calories and macros together. Changing a serving after entering totals can change the resulting nutrition, so check the finished entry rather than relying on the first numbers you typed.

There is no need to scan a meal photo merely to transcribe a label you can read. CalQuest's photo workflow supplies estimates; it is not a barcode or nutrition-label reader. Photo scans use limited free energy, with ads and optional PRO subject to fair use. For repeat products, recheck the current package and your portion before reusing old numbers.

Frequently asked questions

Does per serving mean the whole package?

Only when the stated serving matches the whole package. Check the serving amount and servings per container, or use a clearly labelled per-package column for the whole pack.

How do I calculate 35 g from values per 100 g?

Multiply every relevant per-100 g value by 0.35. This applies to calories and the listed macros. The amount is measured only if you actually weighed the 35 g portion.

Can CalQuest read the nutrition label from a photo?

No. CalQuest does not provide nutrition-label or barcode scanning. Calculate the consumed portion from the package and use manual entry for known nutrition values.

Should I add sugars to total carbohydrates?

No. On the FDA Nutrition Facts label, sugars are already included in total carbohydrate. Use the total carbohydrate value and keep every nutrient on the same serving basis.

Keep exploring

• Compare photos, barcode lookup and manual entry
• Use ingredient labels to calculate a recipe
• Check why two food entries show different numbers
• Understand estimated portions without a scale