How do I calculate peptide concentration when the vial lists content in International Units instead of milligrams?

Check the product insert for the IU-to-mg conversion factor specific to your peptide. For example, if 1mg = 3000 IU and your vial contains 15,000 IU, you have 5mg total (15,000 IU ÷ 3000 IU/mg). Then calculate concentration normally using the mg amount. USP unit conversion standards detail IU calculation methods.