We have refined the CORS method, introduced in 1980 for the computation of the Cepheid radii, in order to extend its applicability to recent and extensive sets of observations. The refinement is based on the computation, from observational data only, of one of the terms of the solving equation, previously based only on precise calibrations of photometric colors. A limited number of assumptions, generally accepted in the literature, is used. New radii are computed for about 70 Cepheids, and the resulting P-R relation is discussed.