How do I calculate the exact peptide mass in solution when accounting for peptide salt forms and hydration?

Many peptides are supplied as acetate, trifluoroacetate, or other salt forms adding 5-30% mass. Check the Certificate of Analysis (COA) for the correction factor. For example, BPC-157 acetate is ~62% active peptide by mass, so a vial labeled '5mg BPC-157 acetate' contains ~3.1mg actual BPC-157. USP salt correction calculations detail conversion methodologies.