How can I convert from international units (IU) to milligrams or micrograms?

1 Answer
Jul 28, 2014

It varies from one substance from another.

The international unit is based on the activity or effect of biologically active substances. Here are some examples.

  • Vitamin A: 1 IU is the biological equivalent of 0.3 μg of retinol or
    of 0.6 μg of beta-carotene.

  • Vitamin C: 1 IU corresponds to 50 μg of L-ascorbic acid

  • Vitamin D: 1 IU is the biological equivalent of 0.025 μg of

  • Vitamin E: 1 IU is the biological equivalent of ²/₃ mg of
    d-alpha-tocopherol or 0.9 mg of dl-alpha-tocopheryl acetate.

  • Insulin: 1 IU is equivalent to 0.0347 mg of human insulin.

For other substances, you may have to consult a pharmacist.


The recommended dietary allowance (RDA) of Vitamin D is 600 IU. What mass of Vitamin D does this represent?


Mass of Vitamin D = 600 IU × #(0.025"µg")/(1"IU")# = 15 µg