In this paper, we proposed a metric for P2P networks based on Shannon's L-channel capacity calculation idea. The metric calculates the maximum rate of information (in bits per second) that can be transmitted over P2P network (a.k.a. combinatorial capacity) caused by protocol and overlay-level connectivity. We suggest P2P systems to be modeled as a discrete noiseless channel on which the protocol together with dynamically changing overlay-level instant connectivity topology defines a Shannon Language. In experimental works, we applied the metric first to the Gnutella 0.6 protocol for which message traffic explosion is a known problem and then to its time-based clustering version. The obtained results are compared with other two known metrics' namely, number of query hits and unit query-hit response time, results and potential correlations among them are discussed.