In some examples, a brake wear measurement system includes an emitter configured to emit a signal and a passive powered sensor system including a controller and a sensor configured to sense the signal emitted by the emitter. The emitter and the sensor of the sensor system are mounted on the brake assembly such as the emitter and the sensor may be configured to move relative to each other as the brake disc stack wears. Thus, a characteristic of the signal emitted by the emitter and sensed by the sensor may change as a function of the brake disc stack wear. The brake wear measurement may further include a processor configured to receive the output generated by the sensor and determine, based on the output, an amount of wear of the brake disc stack assembly.