In this paper we propose that the energy efficiency of wireless sensor networks can be enhanced by optimally selecting number of cluster head in a hierarchical-based routing protocol in a hexagonal topology. The proposed protocol is a variant of famous “Low Energy Adaptive Clustering Hierarchy (LEACH)” protocol and uses probabilistic model in a hexagonal topology to calculate optimum number of cluster heads. In addition to the improvement in energy efficiency, the hexagonal topology gives a better approximation of the realistic propagation environment as the circular coverage region of an omnidirectional antenna is well-approximated by a hexagonal topology. We compare the performance of our proposed protocol through numerical simulations with relevant variant of the LEACH protocol. Results of our numerical simulation results show that the proposed protocol significantly reduces the total energy consumption thereby improving life time of the network.