A single chamber system or apparatus configured to measure a volume of a person, animal, and/or object, and methods of manufacturing and using the same, are disclosed. The system/apparatus includes a chamber having a door thereon or affixed thereto, and a fixed volume therein when the door is closed an oscillating membrane or diaphragm in a wall of the chamber a pressure sensor and/or a pressure transducer configured to measure pressure fluctuations in the chamber and an oscillation amplitude detector coupled to the oscillating membrane or diaphragm. The chamber generally has a volume sufficient to enclose the person, animal, or object therein. The volume of the chamber generally does not vary with relatively small pressure changes or fluctuations.
