To provide a method for simply discriminating size of a pipe joint, in which size error of a joint to a pipe is eliminated, in which work error is eliminated at each part of connection work to the pipe, and in which generation of water leak can be extremely reduced in connection work to water pipes.

This method is for size discrimination to the pipe joint comprising a joint base body to connect the pipe and a socket of resin. The sockets are color-coded by the size. 1: the joint base body, 1a: passage, 1b: step part, 1c: O-ring, 1e: slit, 1f: claw, 2: socket of resin, 2a: inclined inner diameter, 10: pipe.