A thermal, flow measuring device and method for measuring the flow of a measured medium. During a heating phase of predetermined length a constant heating current of a first electrical current source flows through a first resistor. During a first measuring phase of predetermined length a constant measurement current of a second electrical current source flows through the first resistor. During the first measuring phase a first voltage falls across the first resistor, wherein during a second measuring phase of predetermined length during the first measuring cycle the constant measurement current of the second electrical current source flows through a second resistor. During the second measuring phase a second voltage falls across the second resistor, wherein during the heating phase the constant heating current of the first electrical current source flows through a shunt resistor, wherein during the heating phase a fifth voltage falls across the shunt resistor, wherein at least the first voltage, the second voltage and the fifth voltage are utilized for calculating the flow and wherein during the first measuring phase the constant heating current of the first electrical current source flows through a bypass resistor.