The growth of ad hoc networks which occurred in the last few years results in an improvement in routing protocols to handle multi-hop communications. The multi-hop communication is the most suitable solution to overcome the limitation of transmission range of mobile terminals. The selection of routing protocol among the existing ones is a crucial issue, and based on its performance. Thus, in this work the performance of four well-known routing protocols named DSR, AODV, OLSR and DSDV was evaluated based on ad hoc network size (number of nodes). In this work, we have achieved several simulation scenarios to estimate the performance of the mentioned protocols. Results have been achieved by using OMNet++ simulator and we have considered three metrics which are: end-to-end delay, collision and packet delivery ratio for comparison purpose. This metrics are compared based on the number of nodes which have directly affected the number of hops.