An analytical expression that relates the pressure drop, the exchanger area and the film beat transfer coefficient for the shell side of a shell and tube heat exchanger is reported. The equation has been developed based on the Bell-Delaware method, and may aid significantly in tasks such as heat exchanger design and optimization procedures. The mathematical approach used for this formulation can be extended to other heat exchanger systems to provide suitable compact pressure drop relationships. The use of the compact formulation within design and optimization algorithms is illustrated.