Convert vitamin doses between units.
International Units are not a mass unit — they are defined separately for each vitamin by its biological activity, so the IU-to-microgram factor differs from one vitamin to the next. Vitamin D converts at 40 IU per microgram, retinol at 3.33 IU per microgram, and natural d-alpha-tocopherol at 1.49 IU per milligram. Using the wrong factor is how a 1000 IU vitamin D product gets misread as 1000 micrograms, a fortyfold error.
IU to mass conversion by vitamin
mcg = IU / factor; IU = mcg x factor, where factor = 40 for vitamin D, 3.33 for retinol and 0.00149 for natural vitamin E
These figures are population-average estimates for general planning only and are not medical or dietetic advice. Individual energy and nutrient needs vary widely with body composition, activity, medication and health status. Consult a qualified health professional or registered dietitian before making significant changes to what you eat, and especially if you are pregnant or breastfeeding, are under 18, or have a medical condition or a history of disordered eating.
Natural d-alpha-tocopherol is 1.49 IU per milligram while the synthetic dl-alpha-tocopherol form is 1.10 IU per milligram, because the synthetic mixture contains stereoisomers with lower biological activity. This calculator uses the natural form.
It is 25 micrograms, a common maintenance dose. Adult reference intakes are typically 10-20 micrograms (400-800 IU) and the tolerable upper limit is 100 micrograms (4000 IU) a day.
No. Beta-carotene converts to retinol inefficiently, and modern guidance uses retinol activity equivalents where 12 micrograms of dietary beta-carotene equals 1 microgram of retinol. The retinol factor here applies to preformed vitamin A only.