Before trusting a result, check what went into the formula. A calculation can be mathematically correct and still answer the wrong food question. The most useful checks concern identity and measurement rather than how attractive the output looks.
Start with the source basis
Imagine you weighed 75 g of a food, but the label lists values per 50 g. The multiplier is 1.5. Confirm that 75 is the edible food amount, not container-plus-food weight. Confirm that the weighed food is in the preparation state described by the source.
Read every unit
Calories, protein grams and sodium milligrams belong in different fields. A per-100-mL liquid panel cannot be scaled from a gram reading without a product-specific relationship. A percentage is not a gram amount.
Check what is included
A base recipe and optional sauce may have separate totals. A restaurant entry may exclude a side or drink. Make your intended calculation match those boundaries rather than filling a gap with a guessed component.
Keep source status visible
A blank is unavailable. A source-supplied zero has a different meaning. Use current product information and retain the source date where available. FDA’s serving guidance, NIST’s unit references and USDA’s food descriptions support these checks. The 75 g example is invented. If the input basis fails a check, correct that before rerunning the tool; changing the formula cannot turn mismatched evidence into a reliable meal estimate.
Sources and example boundaries
- FDA: serving information
Serving sizes and household/metric units on U.S. labels.
- NIST: units of mass
Gram, milligram and kilogram relationships.
- USDA: Foundation Foods documentation
Food descriptions, portions, missing nutrients and sample variation.
All food figures and prices in the worked example are invented to explain the method. They are not restaurant nutrition, tested recipes, shopping prices or personal dietary advice. Use the current label for the product you actually have.