The unit converter & %DV.
Labels mix IU, mcg, and mg, and "% Daily Value" is easy to misread. Convert vitamin units and check any amount against the FDA's official Daily Value - exact numbers, no guesswork.
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Method & sources
Vitamin unit conversions use the exact factors the FDA applies on Supplement Facts labels - vitamin D: 1 mcg = 40 IU; vitamin A (retinol): 1 mcg RAE = 3.33 IU; vitamin E: 1 mg = 1.49 IU (natural d-alpha) or 2.22 IU (synthetic dl-alpha). The %DV uses the FDA adult Daily Values (21 CFR 101.9) with %DV = amount ÷ Daily Value × 100. The retinol factor applies to retinol, not to beta-carotene, and Daily Values differ for infants, young children, and pregnancy.
- FDA. Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels (Guidance for Industry).
- 21 CFR 101.9 - Nutrition labeling of food (Daily Values; verified against the regulation).
- FDA. Daily Value on the New Nutrition and Supplement Facts Labels.
- NIH Office of Dietary Supplements - vitamin fact sheets.
IU, mcg, mg — what they mean.
IU ("international units") is an old measure of activity, not weight, and the conversion to a metric weight is different for every vitamin. That is why "1000 IU" of vitamin D and "1000 IU" of vitamin E are completely different amounts. The factors this tool uses are the standard published ones:
- Vitamin D: 1 mcg = 40 IU.
- Vitamin A (retinol): 1 mcg RAE = 3.33 IU.
- Vitamin E: 1 mg = 1.49 IU (natural d-alpha) or 2.22 IU (synthetic dl-alpha).
What "% Daily Value" actually is
The % Daily Value on a label compares one serving to a single general reference amount the FDA sets for labeling (the "Daily Value"). It is deliberately one-size-fits-all, so it is a comparison aid, not a personal goal. A %DV over 100% is common and is not automatically a problem - but some nutrients do have safe upper limits, which is a separate question for a healthcare provider.
What this tool isn't
It converts units and computes %DV from public reference numbers. It does not recommend a dose, diagnose anything, or judge whether an amount is right for you. For that, talk to a healthcare provider.