A quantum mechanical methodology, working within the framework of the polarizable continuum model (PCM), yielding quantities directly comparable with data extracted from Kerr experiments of liquids, is presented. The procedure permits us to obtain the final molar property (specifically, the Kerr constant) in terms of effective molecular dipoles and (hyper)polarizabilities. The latter are obtained through an ab initio description of the molecule of interest when it is mutually interacting with the surrounding medium, which is represented by a continuum dielectric. Effects due to the liquid macroscopic polarization yielded by the output wave are also included. Numerical applications, and comparison with experiments, are presented for a selection of pure liquids.