A single block pneumatic gauging system, with an appropriate passageway, receives compressed air to its inlet and its outlet is connected to an air probe. Parts to be gauged, are placed on a fixture which incorporates the air probe. The proximity of the part, to the nozzle of the air probe, creates a restriction which causes the air speed in the passageway to vary proportionally to the size of the part. A transmitter, at the mid-point of the passageway, generates a sonic wave, which propagates in the passageway. A receiver at the inlet will sense the sonic wave which travels at the speed of sound minus the air speed and a receiver at the outlet will sense the sonic wave which travels at the speed of sound plus the air speed. Phase comparison of both waves provides a signal proportional to air speed in the passageway which in turn is proportional to the size of the part being gauged.