A device and method are described for precisely measuring pulmonary ventilation without the need for mouthpiece, face masks or other inhibiting devices subsequent to calibration. Anterior-posterior and lateral displacement of both the rib cage and abdomen are measured during breathing by at least 4 sets of magnetometers. The signals from the magnetometers are fed along with an initial signal from a breath volume measuring device to a microprocessor which correlates these signals by a least squares analysis to give constants defining the relationship between the magnetometer signals and readouts of total ventilation; respiratory rate, tidal volume and relative proportion of rib cage versus abdomen volume. Once the device is calibrated, these parameters can readily be determined independently of any direct measurement of breath volume. It has been found particularly important that calibration be performed during rebreathing at volumes of 1-2 liters of air, breathed 3-6 times to reduce the noise to signal ratio.