According to e-Tool Age, there are 73.5 mg in 100 IU of natural vitamin E. There are 100 mg contained in 100 IU of synthetic vitamin E.
IU stands for international units. It is used for the measurement of drugs and vitamins. Defined as a quantity of a biologic that produces a biological effect, such as a vitamin, this measurement is an international standard. Dependent on the potency of a vitamin or other substance, each individual substance has a different IU to mg conversion. Knowing the synthetic, natural and alpha tocopheryl/tocopherol compositions of the vitamin E in question, yields the most accurate IU to mg conversions.