Step‐growth polymerized systems of general type “AfiBgi” are considered. One or more of the monomer species carries at least three reactive groups and thus can act as a branching point in a polymeric molecule. An algorithmic method is presented to calculate the topology‐averaged square radius of gyration, R
2[s], of the molecules in the class of s‐mers. The degree of polymerization, s, may run through its full range. In addition to R
2[s], the shrinking factor, g[s], is calculated. The method uses integer arithmetic, generating functions, and computer algebra.