Skip Navigation

Unit Conversions

This table provides conversion factors from Percent Daily Value units as found on Supplement Facts panels on dietary supplements products to units consistent with the Daily Reference Intake values.

Nutrient Daily Value Unit DRI Equivalent Units
Vitamin A 1 IU (International Unit) = 0.3 microgram (µg) as retinol
= 0.6 microgram (µg) as beta-carotene
Vitamin D 1 IU (International Unit) = 0.025 microgram (µg) cholecalciferol or ergocalciferol
Vitamin E 1 IU (International Unit) = 0.67 milligram (mg) for d-alpha-tocopherol (natural)
= 0.9 milligram (mg) for dl-alpha-tocopherol* (synthetic)

* Explanation of Vitamin E unit conversion:

For the DSID, the results from the chemical analysis of vitamin E (as alpha-tocopherol) in dietary supplements are reported by the laboratory in mg/g. This amount is converted to IU/serving using the weight of one serving of the product in grams and applying the appropriate conversion factor. The analytical result in IU is then compared to the label value in IU to calculate the percent difference from the labeled amount. The conversion factor used for each analytical result is dependent upon whether the alpha-tocopherol being measured is in a natural or synthetic form.

Current manufacturing guidelines provided by the FDA are based on the 1968 RDAs (Recommended Daily Allowance), which use a factor of 0.9 for converting synthetic vitamin E as dl-alpha tocopherol from IU to mg. In contrast, the 2003 Dietary Reference Intake (DRI) guidelines are based on bioavailability standards for converting the quantity of synthetic vitamin E as dl-alpha-tocopherol from IU to mg, which is IUx0.45.

For natural vitamin E as d-alpha-tocopherol, the conversion of IU units to mg units is the same for both FDA labeling guidelines and the 2003 DRI, using IUx0.67.