A method of auto-calibrating aircraft cabin pressure sensors in a cabin pressure control system while in service, wherein at a constant sensed cabin pressure during a cruise flight phase at least one pressure sensor output voltage from each of two cabin pressure sensors are recorded. Upon landing and opening of the cabin doors the sensed cabin pressure value is compared to an external field pressure. A new software slope variable and a new software offset variable are computed for the pressure/voltage function using an average computed pressure value in cruise and the recorded field atmospheric pressure sensor voltage value on the ground. Thereafter, a new cabin pressure value is calculated and control software is modified.