Things You'll Need
Instructions
Find the definition of the weight of the drug, vitamin or supplement of interest required to show the level of biological effect. This definition indicates the weight for an International Unit value of 1. This information is a literature value that you can locate by contacting the manufacturer of the chemical.
Convert the number of ng in the sample to milligrams. Most definitions of an IU are defined in terms of mg. Use the conversion factor of 1 mg = 10^6 ng. For example, find the number of mg of insulin in a ml of a solution containing 182 ng of insulin. 1 mg equals 10^6 ng. Convert the ng to mg by dividing by 10^6. The result is 0.000182 mg.
Divide the weight of the particular vitamin, drug or supplement in mg by the number of mg equivalent to one IU. The result equals the number of IU's of the substance you have. Continuing the example, assuming 1 IU of insulin is 0.0455 mg, mg of sample / mg per IU = 0.000182 / 0.0455 = 0.004 IU.