Vitamin IU converter
Convert international units to micrograms. Pick the vitamin first: an IU is a unit of activity, so every vitamin converts differently.
That's 1.67× as much as a daily requirement, while a typical supplement is 2× more. Information only: check the form stated on your own label.
What it means
How much is that?
Information only, not medical advice. Labels increasingly give micrograms instead of IU, and for vitamin E the natural and synthetic forms differ.
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Three things worth knowing
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1,000 IU of vitamin D = 25 µg
The common 1,000 IU capsule is 25 micrograms, and 4,000 IU is 100. Multiply IU by 0.025 for vitamin D and nothing else.
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Before anyone could weigh a vitamin
In the 1930s vitamins could not be purified reliably, so potency was defined by what a dose did to a test animal. The IU is what is left of that system.
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Natural and synthetic vitamin E differ
1 IU is 0.667 mg of the natural d-alpha form but 0.9 mg of the synthetic dl- form. The same IU number means different milligrams on different bottles.
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Background
About international units
An international unit measures biological activity, not weight. It was invented so that preparations of unknown purity could be compared before anyone could weigh a vitamin accurately.
Because each vitamin has its own definition, there is no single conversion: 1 IU of vitamin D is 0.025 µg, but 1 IU of vitamin A is 0.3 µg of retinol.