A mass flow controller (MFC), a method for calibrating an MFC, and a method for operating an MFC are disclosed. The method for calibrating the MFC includes obtaining data relative to two signals from a thermal mass flow sensor when operating the mass flow controller at different flow rates with a calibration gas, and storing the data relating to the two signals in connection with corresponding flow-rate values. The method for operating the MFC includes obtaining data relative to the two signals from the thermal mass flow controller and accessing the calibration data to determine an unknown flow rate for a process gas that may be the same gas as the calibration gas or may be another gas that is different from the calibration gas.