A general procedure for heat exchanger design has been presented in the Heat Exchanger Design Handbook (HEDH), but no precise criterion for determining the baffle spacing has been offered, and the emphasis is only on its permissible range of application. In this paper, an optimization program has been used to calculate the optimum baffle Spacing and the number of sealing strips for all types of shell and tube heat exchangers, using the procedure in HEDH. A set of correlation is presented for determining the optimum baffle spacing. This could be considered as complementary to the HEDH recommendations.