A sensor unit for measuring a mass flow rate of a liquid hot-melt adhesive is disclosed. The sensor unit includes a flow channel for the hot-melt adhesive, a first temperature measurement device positioned at a first position in the flow channel, a second temperature measurement device positioned at a second position in the flow channel and a heating device assigned to the second temperature measurement device, and a control unit for controlling the heating device and for measuring the mass flow rate. The controller is configured to adjust the temperature of the heating device assigned to the second temperature measurement device to a value, to determine the heating power for heating the heating device assigned to the second temperature measurement device, and to calculate the mass flow rate in the flow channel. The first and second temperature measurement devices are arranged substantially parallel to each other in the flow channel.