21 CFR 101.9
Nutrition labelling of food, including the rounding rules in 101.9(c) and the serving-size procedures in 101.9(b). Read from the official CFR text published by GovInfo.
Resources
What the tools are built on.
Short and honest: the primary sources behind the calculators, and the services for people building software. There are no guides or courses here yet. When there are, they will be listed on this page.
Primary sources
The calculators implement published rules rather than someone's interpretation of them. These are the documents they are built from, so you can check any figure yourself.
21 CFR 101.12 Table 2
The 140 reference amounts customarily consumed (RACC) that serving size is derived from. The Food Business Toolkit reproduces the published column verbatim and never alters it.
USDA FoodData Central
The nutrient database behind the Nutrition Facts Label Calculator. Public, versioned, and citable — which is why the tool uses it rather than a scraped table.
Always check the current rule
The CFR annual edition is a point-in-time codification and regulations change. Confirm your own category against the current eCFR before printing a label. These tools help you apply a published procedure; the declaration on your package remains yours.