Method and apparatus for volume measurement and body composition estimation provides an accurate, non-invasive estimation of the body volume and body composition of an object or body such as a human being. The present invention provides a first chamber (2) with a door (9) or closable means of entry through which an object or a subject may enter, along with a second chamber (3) and means (18) to cyclically perturb the volumes of the two chambers in a precisely complementary fashion. The present invention also measures the pressure in each of the chambers, controls in real time the volume perturbation and analyzes the pressure records so as to yield volume and body composition estimations.