The sum of 50,000 international units of vitamin D is equal to 1.25 milligrams. This conversion is based on the conversion formula provided by the U.S. National Institutes of Health.
The formula for converting international units to milligrams applies to both forms of vitamin D that are available as supplements. These two forms are D2 and D3, as stated by the NIH. The specific formula the NIH provides shows that the number of international unites divided by 40 is equal to one microgram. One microgram is equal to 0.001 of a milligram, as stated by the NIH.
The conversion formula for converting international unites of vitamin D to milligrams should not be applied to other substances, such as vitamin A or vitamin C. Each substance has it own conversion formula, according to the NIH.