A device that automatically detects the strength of the paper as an indicator of paper weight and thickness. The detector includes a deflector acting on the paper or other sheet media and a deflection sensor that is responsive to the deflection of the paper. The deflector may be gravity or a mechanical device, or a combination of both. A mechanical deflector typically will include a contact member and a gate member. The contact member is biased against and deflects the sheet media advancing past the detector. The sensor is in operative communication with the gate member of the deflector. The deflector is operative to move between a first position, wherein the sensor outputs a first signal, and a second position, wherein the sensor outputs a second signal.