A novel method is presented for the calculation of weight chain length distribution in free radical polymerization of vinyl monomers. In the proposed method, polymerization kinetic equations and molecular weight moment equations are used in conjunction with a function that defines the weight fraction of polymer in a finite chain length interval. The entire range of molecular weight is divided into a finite number of intervals, and the weight fractions of polymers in these intervals are calculated. It is also possible to predict a chromatogram obtainable by gel permeation chromatography. A numerical example is presented and compared with experimental data to illustrate the usage of the proposed method.