This paper proposes a zone radius determination algorithm for the independent zone routing protocol based on the number of one-hop neighbors. Optimal zone radius lies where the number of control packets is minimized. Legacy zone radius determining algorithms cause unnecessary costs such as a long network set up time and unstable changing point. Each node counts one-hop neighbors then estimates intrazone routing protocol (IARP) packets to be generated. Simulation shows the proposed algorithm enables each node to estimate the control packets and to change the radius fast.