Updated 13 October 2026: This article has been reviewed and revised for clarity and label-reading accuracy.
A label can show grams, milligrams and percentages within a few lines. They are not interchangeable. Grams and milligrams measure an amount by mass; percent Daily Value compares a nutrient amount with a reference for that nutrient. Copying the number without its unit can change the meaning completely.
This guide explains the arithmetic behind U.S. label entries. The examples do not set personal nutrient targets.
Convert units before comparing amounts
One gram equals 1,000 milligrams. To turn grams into milligrams, multiply by 1,000. To turn milligrams into grams, divide by 1,000.
| In grams | In milligrams |
|---|---|
| 1 g | 1,000 mg |
| 0.25 g | 250 mg |
| 0.04 g | 40 mg |
For an invented comparison, a note showing 0.25 g of a nutrient and another showing 250 mg describe the same mass. Reading 250 as automatically larger than 0.25 would be a unit error. Write the conversion on a separate line, then compare the values in one unit.
Converting to a common unit does not make different nutrients equivalent. Two grams of dietary fiber and two grams of sodium have the same mass, but that fact does not give them the same dietary meaning. Keep the nutrient name beside the unit.
A percentage needs its own reference amount
The FDA’s Daily Value reference guide lists different reference amounts for different nutrients. For example, sodium uses 2,300 mg and calcium uses 1,300 mg in the standard table. To explain the percentage mathematically, divide the nutrient amount by its own reference and multiply by 100.
- 230 mg sodium ÷ 2,300 mg × 100 = 10% DV.
- 130 mg calcium ÷ 1,300 mg × 100 = 10% DV.
Both results are 10%, although the milligram amounts differ. The percentage tells you about the relationship to each nutrient’s reference. It is not a claim that the two nutrients weigh the same or serve the same role.
Do not add percentages down the label
Imagine a serving with 10% DV sodium and 10% DV calcium. Adding them to get 20% produces no useful overall nutrition score. You have mixed two different reference systems. Record the entries separately and compare each nutrient with the matching entry on another product.
Similarly, a threshold stated in grams for one nutrient cannot be transferred to another nutrient simply because both are on the label. The useful comparison depends on what the nutrient is, how much food the entry describes and which reference is being used.
Use a three-part check for every copied number
- Name: Which nutrient is this?
- Unit: Is the number in g, mg, another unit, or %DV?
- Basis: Is it per serving, per package, or another stated amount?
For example, “sodium, 230 mg, per serving” contains enough information to start a calculation. “230, 10%” does not. When your source is a cropped image, recover the missing headings before calculating.
A useful final check is to reverse a unit conversion: 250 mg divided by 1,000 should return 0.25 g. If the conversion does not return to the starting amount, fix it before drawing a conclusion about the product.
Source
FDA: Daily Value on the Nutrition and Supplement Facts Labels, including its nutrient reference table and unit key.
