Abstract The calculation formula of electro-kinetic potential (also called zeta potential) with electrophoresis method was confused in current textbooks of physical chemistry and experiments in physical chemistry due to using different systems of units. In this work, the physical meanings of the different dielectric constants and the right calculation formula of zeta potential under CGSE units and SI units were discussed based on the literature survey. Moreover, it was summarized with the unified calculation formula of zeta potential for all the colloidal particles along with the calculated examples verification.
