Abstract: A flow gauge for measuring the mass flow rate of freely flowing material, falling through a path, said flow gauge comprising a pair of sensors spaced longitudinally along the chute, the sensors being connected to a computing means for receiving the output of each sensor, where said output is a measure of the density of the flow at the location of the sensor, the computing means utilizing the output of the sensors to provide a measure of the mass flow rate, said sensors comprising a radiation source and a radiation detector in opposed relation to the source and on the other side of the flowing material from the detector, for detecting the radiation passing through the flowing material.