IU to mg / mcg Converter for Vitamins
International Units (IU) measure activity, so each vitamin has its own conversion factor. Pick the vitamin, enter IU.
Conversion factors
| Vitamin | 1 IU equals |
|---|---|
| Vitamin D (D2 or D3) | 0.025 mcg |
| Vitamin E — natural (d-alpha-tocopherol) | 0.67 mg |
| Vitamin E — synthetic (dl-alpha-tocopherol) | 0.45 mg |
| Vitamin A — retinol | 0.3 mcg RAE |
| Vitamin A — supplemental beta-carotene | 0.3 mcg RAE |
| Vitamin A — dietary beta-carotene | 0.05 mcg RAE |
Factors from the NIH Office of Dietary Supplements fact sheets: vitamin D, vitamin E, vitamin A. Vitamin A factors are given in mcg RAE (retinol activity equivalents).
Vitamin D IU to mcg chart
| IU | mcg |
|---|---|
| 400 IU | 10 mcg |
| 600 IU | 15 mcg |
| 800 IU | 20 mcg |
| 1,000 IU | 25 mcg |
| 2,000 IU | 50 mcg |
| 4,000 IU | 100 mcg |
| 5,000 IU | 125 mcg |
| 10,000 IU | 250 mcg |
| 50,000 IU | 1,250 mcg |
US Supplement Facts labels now list vitamins D, E and A in mcg or mg; many still show IU in parentheses.
FAQ
How do I convert vitamin D IU to mcg?
1 IU of vitamin D = 0.025 mcg, so divide IU by 40. Example: 1,000 IU = 25 mcg; 2,000 IU = 50 mcg.
How many mg is 400 IU of vitamin E?
It depends on the form: natural d-alpha-tocopherol is 0.67 mg per IU (400 IU = 268 mg); synthetic dl-alpha-tocopherol is 0.45 mg per IU (400 IU = 180 mg).
Why is there no single IU to mg conversion?
An IU measures biological activity, which differs for every substance and even between forms of the same vitamin, so each one has its own factor.
Can I use this for products other than vitamins D, E and A?
No. Other substances labeled in IU have different factors or no general mg equivalent; follow the product label.
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