International unit

An International unit (IU) is a unit of measurement in pharmacology. It is based on measured biological activities.

The equivalents of 1 IU for some vitamins:

Vitamin A (retinol equivalents)	0.3 micrograms
Vitamin C	50 micrograms
Vitamin D (cholecalciferol/ergocalciferol)	0.025 micrograms
Vitamin E (alpha tocopherol equivalents)	0.666 (2/3) milligrams

An alternative abbreviation for International Unit is UI.