This research tests the relative ability of body size factors and sex to explain variation in nose volume and to explain metabolic measures during rest and moderate exercise in 50 young adults. It uses standard anthropometric measures plus two new measures of nose morphology (nose/face angle and nose volume) and evaluates body composition with a device for air displacement plethysmography. Standard physiological measures were obtained in nose-only and mouth-only breathing conditions with subjects at rest and using moderate exercise. A factor representing linear and bulk measures of body size and a factor representing lean body mass explain subjects' variation in nose volume, resting volume of oxygen consumed (VO2), and resting ventilation volume (VV) better than subject's sex does. By contrast, during exercise, sex explains VO2 and VV better than do body size factors, probably because hormone-mediated muscularity in males produced greater work output. Nose breathing was found to be more energetically efficient in most but not all subjects, but additional research is needed to explore this finding further. Qualitative comparisons between modes of breathing and the application of this research protocol to studies of climate-related patterns of nasal variation are discussed.