A mass flow rate sensor uses a Reynolds number correction function to compensate for errors in a bypass ratio of the sensor for all gases, based on the fact that all bypass errors are functions of Reynolds number. The sensor includes a sensor tube and a bypass tube dividing flow, wherein a bypass ratio of the sensor equals a total flow rate through the sensor divided by a flow rate through just the sensor tube. Heater elements heat an upstream portion and a downstream portion of the sensor tube, and a circuit is connected to the heater elements for producing a voltage based upon a difference in resistance between the heater elements. The voltage is calibrated based on known flow rates of a reference gas, and the flow rate through the sensor is based upon the calibrated voltage multiplied by a multi-gas correction function and a Reynolds number correction function.