Before using a calorie number, find what it describes: 100 g, one serving or the whole package. Accurately copying the wrong basis still produces an incorrect food log.
Start with the serving size
Label formats vary by country. On a US Nutrition Facts label, the listed serving size describes the basis of the values; it is not a personalised recommendation. Read the label on the actual product rather than assuming a familiar package has the same recipe everywhere.
Example 1: calories per 100 g
Suppose a label gives 420 kcal per 100 g and you eat 30 g. The calculation is 420 × 30 ÷ 100 = 126 kcal. If the app asks for grams, enter 30 g. If it asks directly for energy, the portion is 126 kcal, not 420 kcal.
Example 2: several servings per package
Suppose a package contains four servings at 90 kcal each. One quarter of the package is 90 kcal, half is 180 kcal and the whole package is 360 kcal. These are illustrative numbers, not a real product. Use the label’s stated weight to check the amount.
Compare on the same basis
Comparing a 20 g serving of one product with a 50 g serving of another can mislead. Convert both to the same weight before comparing, then consider your actual portion. Read the ingredient list and nutritional information alongside front-of-pack claims.
Check the app entry
Match the exact product, preparation and amount. A photo suggestion is a starting point and may need correction. For unpackaged food, use the food reference library and account for additions.
See the FDA guide to the Nutrition Facts label for the US format.
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