Catch the thousandfold error when comparing mg and g
Match mass units before comparing nutrient amounts, then keep serving-size adjustments separate from unit conversion.
Milligrams and grams both measure mass, but one gram contains one thousand milligrams. A comparison can be wrong by a factor of one thousand even when both copied numbers are otherwise correct. Write the unit next to the value before entering it into a calculator.
The FDA Daily Value reference displays nutrients using different mass units. This article concerns unit arithmetic, not the reference amounts or how much of a nutrient a person should consume.
Convert the same nutrient to one unit
Imagine two hypothetical records for the same nutrient and the same 50 g portion. Record A says 250 mg; record B says 0.4 g. Convert B to milligrams: 0.4 × 1,000 = 400 mg. The difference is 150 mg per 50 g portion, with B having the larger declared amount.
Comparing the bare numbers 250 and 0.4 would reverse that conclusion. Converting A instead gives the same answer in grams: 250 ÷ 1,000 = 0.25 g, so the gap is 0.15 g. There is no nutritional change when you switch units; only the numerical representation changes.
Use a two-stage worksheet
Now suppose A's 250 mg applies to 50 g of food, while B's 0.4 g applies to 80 g. First convert B to 400 mg. Then normalize the portions: A is 250 ÷ 50 × 100 = 500 mg per 100 g, and B is 400 ÷ 80 × 100 = 500 mg per 100 g.
The two records now have equal calculated concentrations. The earlier difference in portion amounts was real within the hypothetical records, but it did not show a difference at equal food weight. Keeping unit conversion and portion conversion in separate columns makes this visible.
Audit the labels on your fields
- Preserve the original value and unit in a source column.
- Use one chosen nutrient unit for the entire comparison.
- Keep the food weight separate from the nutrient mass.
- Check that both rows refer to the same nutrient, not salt in one and sodium in the other.
A g-to-mg conversion cannot translate one substance into another. Nor can it turn millilitres of a drink into grams of that drink. Those are different questions requiring additional information beyond a decimal shift.