Since energy consumption is one of the main challenges in wireless sensors networks performance and efficiency, this paper discusses and proposes a mathematical model that compromises these two crucial parameters. In addition, number of clusters, cluster size, and number of cluster heads all contribute in network robustness; they have been studied and manipulated in details. This paper suggests a mathematical model that calculates and finds the optimal cluster size and number of sensors for Low Energy Adaptive Cluster Hierarchy (LEACH) protocol. Wireless Sensor Network (WSN) is a network includes devices (sensors) for collecting data by sensing the field. Clustering is one of the simplest strategies used to minimize the power lost in WSNs. Its performance is affected by network area and number of sensors. The cluster head is elected based on traditional Low Energy Adaptive Cluster Hierarchy protocol. The optimal cluster number is detected based on the condition of the LEACH delivery ratio. NS2.35 and MannaSim framework are applied for validating the proposed model. The results show that the proposed model is approved at different areas and nodes density. The optimal cluster size obtained by the proposed model is equivalent to optimal clusters number for 100 % delivery ratio of LEACH.