<P> In pharmacology, the international unit is a unit of measurement for the amount of a substance; the mass or volume that constitutes one international unit varies based on which substance is being measured, and the variance is based on the biological activity or effect, for the purpose of easier comparison across substances . International units are used to quantify vitamins, hormones, some medications, vaccines, blood products, and similar biologically active substances . </P> <P> The name international unit has often been capitalized (in English and other languages), although major English - language dictionaries treat it as a common noun and thus use lower case . The name has several accepted abbreviations . It is usually abbreviated as IU in English, UI in Romance languages (for example Spanish unidad internacional, French unité internationale, Italian unità internazionale, Romanian unitate internațională), IE in several Germanic languages (for example German internationale Einheit, Dutch internationale eenheid) or as other forms (for example Russian МЕ, международная единица (mezhdunarodnaya jedinica), Hungarian NE, nemzetközi egység). In order to remove the possibility of having the letter "I" confused with the digit "1", some hospitals have it as a stated policy to omit the "I", that is, to only use U or E when talking and writing about dosages, while other hospitals require the word "units" (or words "international units") to be written out entirely . </P>

What is the measurement of iu compared to mg