Abstract: In a system for measuring the volume of a closed air space as for example the volume of the air space above the liquid in a container, a regulated gas supply provides a source of predetermined pressure which is used to charge a small vessel of known volume to the same pressure. A fluidic sensing system detects when the pressure in the vessel is equal to the pressure of the regulated supply and then automatically interrupts the connection between the gas supply and the vessel and then connects the vessel to discharge into the volume being measured. The resulting pressure in the volume will be inversely proportional to the volume.