Percent Daily Value is not the percentage of the food
Distinguish grams from %DV with a worked fibre example, then compare two labels without mixing their denominators.
If a label says 10% Daily Value for a nutrient, that does not mean the food is 10% that nutrient by weight. The two percentages divide by different things: one uses a daily reference amount; the other would use the weight of the food.
The FDA describes Daily Values as reference amounts and %DV as the share supplied by a serving. For adults and children aged four and older, its table lists 28 g as the Daily Value for dietary fiber. FDA Daily Value reference. The FDA's general label-reading guide treats 5% DV or less as low and 20% DV or more as high per serving. FDA label-reading guide.
Follow the denominator
Imagine a 40 g serving of a fictional cereal contains 2.8 g of fiber. Relative to the 28 g daily reference, 2.8 ÷ 28 × 100 = 10%. Relative to the weight of the cereal, 2.8 ÷ 40 × 100 = 7 g per 100 g. These calculations answer different questions and do not contradict each other.
Manufacturers display rounded label values, so a calculation from the printed grams will not always reproduce the printed percentage exactly. Use this example to understand the relationship. It is not a method for auditing whether a manufacturer's label meets all applicable requirements.
Compare products with equal amounts
Suppose cereal B lists 4.2 g of fiber per 60 g serving. That works out to 4.2 ÷ 28 × 100 = 15% of the reference, but also 4.2 ÷ 60 × 100 = 7 g fiber per 100 g. Both cereals have the same calculated fiber concentration despite the different daily percentages for their stated servings.
If you pour 50 g of either cereal, the amount is 7 × 50 ÷ 100 = 3.5 g fiber. You can save that as the result for your chosen portion. It does not specify how much fiber you personally need or how the rest of your day's meals should be arranged.
Do not copy a percentage into a grams field
For the comparison calculator, enter the nutrient amount and its mass unit, plus the food's serving weight. A printed 10% is not 10 g. If you only have a percentage and lack the underlying amount or relevant reference, return to the full label before calculating.
Also keep the market attached to your notes. Reference values and label formats may differ. Two percentages on labels from different systems are not automatically comparable. A compact record such as “2.8 g fiber per 40 g serving; US label; checked on this package” preserves more useful information than a percentage alone.