This paper is devoted to test the size-density hypothesis in classical p-median problems in which the sum of users' travel distance is minimized. It is known that multisource Weber problems on a continuous plane show the relationship that the facility size is proportional to the demand density raised to the one-third power. By using numerical examples, we show that the relationship sufficiently holds also in large size p-median solutions with the Delaunay network. We lose somewhat this relationship with less connected network such as the minimum spanning tree or an actual network, but some relationship still exists between the facility size and the demand density. This rule can be applied to seeking approximate solutions of p-median problems.