💊 mcg to IU Converter
Convert between micrograms (mcg) and International Units (IU) for common vitamins, using the standard conversion factor for each one.
Why the conversion factor changes by vitamin
International Units (IU) measure biological activity, not mass, so the mcg-to-IU conversion factor is different for every vitamin and even for different chemical forms of the same vitamin. This converter uses the standard accepted factors: 1 mcg of Vitamin D equals 40 IU, 1 mcg RAE of Vitamin A (retinol) equals about 3.33 IU, and Vitamin E differs by form (natural d-alpha-tocopherol is about 1.49 IU per mg, while synthetic dl-alpha-tocopherol is about 1.1 IU per mg).
How to use it
Enter the amount, choose the vitamin and form, and select whether you’re converting from mcg to IU or from IU back to mcg. The calculator applies the matching factor automatically.
This tool is for general educational and label-reading purposes only. Always check product labels for the specific form used and consult a healthcare provider or registered dietitian before changing any supplement routine.