A method for delivering a process gas to a reaction chamber of a plasma processing system using a recipe having a recipe flow rate is provided. The method includes delivering the process gas by a gas flow delivery system controlled by a mass flow controller (MFC) to an orifice. The predicted flow rate is previously computed by pressurizing a gas. The predicted flow rate further being previously computed measuring a set of upstream pressure values of the gas via at least one pressure sensor. The method also includes applying, using a programmed computing device, a calibration factor of a set of calibration factors to determine the predicted flow rate, the calibration factor being a ratio of an average of the set of upstream pressure values to an average of a set of golden upstream pressure values.