This technical note provides a transparent, source-referenced derivation of the molar weight conversion factor (1.27) used to calculate equimolar doses of EIDD-1931 (N4-hydroxycytidine, NHC) from established EIDD-2801 (molnupiravir) dosing schedules. The factor is a standard stoichiometric ratio derived from the confirmed molecular weights of EIDD-2801 (329.31 g/mol) and EIDD-1931 (259.22 g/mol), verified via PubChem (NIH) and corroborated by peer-reviewed publications in high-impact journals. The document explains the prodrug–active metabolite relationship, the esterase-mediated hydrolysis mechanism, and provides first-principles verification of both molecular weights using IUPAC atomic weights. Prepared to support accurate equimolar dosing calculations in feline medicine, with application to conditions including feline infectious peritonitis (FIP), feline calicivirus (FCV), feline gingivitis, and feline chronic gingivostomatitis (FCGS).