In general, wireless mesh networks provides wireless Internet access service to client terminals that exist in the coverage area of the network. In such networks, the coverage area size and its overlap degree have a significant effect on network performance. In order to determine the coverage area size for each node, it is important to use the location information of neighboring nodes. However, such information cannot be always obtained. In the present paper, we introduce the method to determine the coverage area size only by utilizing the distance information estimated from received signal strength. Specifically, in proposed method, each node estimates the relative locations of its neighboring nodes based on the estimated distance information. It then calculates its Voronoi area, and sets its coverage area size based on the shape of Voronoi area. We conduct simulation experiments to evaluate the performance of the proposed method in terms of total covered ratio, coverage overlap, and energy consumption. We confirm that our method can keep more than 99% of total covered ratio regardless of the node density and reduce the energy consumption more than 50% than that of existing method.