Devices, methods, and systems for monitoring thickness uniformity are described herein. One system includes a transmitter configured to transmit a signal through a portion of a material while the material is moving, an attenuator configured to absorb a first portion of the transmitted signal, a reflector configured to reflect a second portion of the transmitted signal, a receiver configured to receive the reflected signal, and a computing device configured to determine a thickness of the portion of the material based on a time delay between the transmission of the signal and the reception of the reflected signal