A pipe coupler includes a first jaw member, a first jaw extension, a second jaw member defining an open channel, a mounting board, a ratchet, and a first biasing member. The first and second jaw members are hinged to each other. The mounting board extends outwardly from the open channel of the second jaw member. The first jaw extension extends from the first jaw member, and is configured to extend into the open channel. The first jaw extension has a plurality of rack teeth. The ratchet is rotatably mounted on the mounting board, and has a plurality of ratchet teeth configured to mesh with the rack teeth. The first jaw extension is permitted to drive the ratchet to rotate unidirectionally against a first biasing force of the first biasing member.