A US Nutrition Facts label is a legal document with rules behind every line. Knowing a few of them makes it much easier to read, and to know how far to trust it. This article covers the US label as the Food and Drug Administration (FDA) describes it.
The short version
- Check serving size and servings per container first. Every number below them is for one serving.
- Percent Daily Value (%DV): 5% or less per serving is low, and 20% or more is high.
- Labels are rounded and allowed some error. Calories can run up to 20% over before a food counts as misbranded.
Step 1: serving size and servings per container
The FDA's example is a lasagna with a serving size of 1 cup and 4 servings in the package. The label shows 280 calories per serving, so eating the whole package is 1,120. A serving size is not a recommendation of how much to eat. It is the reference amount the numbers are for. Most mistakes happen here: a bag that "has 2.5 servings" is easy to finish in one go.
Step 2: calories
The label uses 2,000 calories a day as a general guide, and the FDA says your own needs depend on age, sex, height, weight and activity. The calorie calculator estimates yours.
Step 3: percent Daily Value
%DV tells you how much one serving adds toward a day's reference amount, based on a 2,000-calorie diet. The FDA's rule of thumb is that 5% or less is low and 20% or more is high. The reference amounts are:
- Saturated fat: 20 g, and the goal is less than that.
- Sodium: 2,300 mg, and the goal is less than that.
- Added sugars: 50 g, and the goal is less than that. The label separates added from natural sugars: the FDA's yogurt example has 7 g of added and 8 g of natural sugars, 15 g in total.
- Fiber: 28 g, and the goal is at least that. The FDA notes that Americans generally do not get enough fiber, vitamin D, calcium, iron or potassium.
These are reference amounts for a population, not targets for your calories or your body.
Step 4: protein, carbs and fat in grams
Grams turn into calories at 4 a gram for protein and carbohydrate and 9 for fat, the general factors in the US labeling rules (21 CFR 101.9). Total carbohydrate is worked out by subtraction: what is left of the food's weight after protein, fat, water and ash. That is why it includes fiber.
A worked example
A granola label says 8 g fat, 29 g carbohydrate and 6 g protein per serving.
- 8 x 9 = 72, 29 x 4 = 116, 6 x 4 = 24. Total 212 calories.
- The rule rounds calories above 50 to the nearest 10, so the label says 210.
- The label's calories and its own grams can differ by a few calories, and that is legal.
The rounding rules
- Calories go to the nearest 5 up to 50, and the nearest 10 above that. Under 5 may be listed as zero.
- Total fat goes to the nearest 0.5 g below 5 g and the nearest gram above 5 g. Under 0.5 g is listed as zero.
- Carbohydrate and protein go to the nearest gram, and under 0.5 g may be listed as zero.
So "0 g" can mean up to nearly half a gram per serving. Several servings of a "zero" food add up.
What we are less sure about
- How exact a label is. For calories, sugars, fats, cholesterol and sodium, a food counts as misbranded when lab values run more than 20% above the label, with some allowance for the variability of lab methods. A label is a regulated average, not a measurement of your package.
- Calories do not always equal 4-4-9. The rules allow either the general factors or more specific ones, so two foods with the same grams can carry different calories.
- %DV fits a 2,000-calorie diet. If you eat much more or less, the percentages are not your percentages.
- The database behind an app. Barcode data in Vital comes from Open Food Facts, which people and companies fill in. Vital compares an entry's calories with its own protein, fat and carbs, shows a notice when they are far apart, and lets you edit the numbers. That catches typos, not a product whose numbers are consistently wrong.
Sources
- U.S. Food and Drug Administration. How to Understand and Use the Nutrition Facts Label. Content current as of March 5, 2024. fda.gov
- Code of Federal Regulations, Title 21, section 101.9: Nutrition labeling of food (Cornell Legal Information Institute copy). 21 CFR 101.9
- U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025, Appendix 7: Nutritional goals for age-sex groups. PDF
- U.S. Department of Agriculture. FoodData Central, SR Legacy data (public domain). fdc.nal.usda.gov
Written November 5, 2026. This is general information, not medical advice. Talk to a doctor or dietitian before big changes to how you eat or train, especially with a medical condition or a history of disordered eating.