A combination vacuum gauge provides simultaneous absolute and differential pressure measurements over a wide-range of pressures ranging from atmospheric pressures to ultrahigh vacuum by processing the readings of (i) an absolute high vacuum gauge (e.g., an ionization gauge and/or a heat-loss sensor) and an absolute or a differential low vacuum gauge (e.g., a diaphragm sensor) exposed, through a common port, to pressures in a measurement region, and (ii) a barometric absolute pressure sensor exposed to the ambient atmosphere outside the measurement region. The barometric absolute pressure sensor reading may be used to convert the differential vacuum gauge reading from uncalibrated differential pressure to calibrated absolute pressure or to convert the absolute vacuum gauge reading from absolute pressure to differential pressure.