Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Vital capacity is the maximum volume of air that a person can exhale after maximum inhalation. It can also be the maximum volume of air that a person can inhale after maximum exhalation.
A person's vital capacity can be measured by a spirometer which can be a wet or regular spirometer. In combination with other physiological measurements, the vital capacity can help make a diagnosis of underlying lung disease.
Vital capacity is the maximum amount of air a person can expel from the lungs after first filling the lungs to their maximum extent and then expiring to the maximum extent (about 4600 milliters). It equals the inspiratory reserve volume plus the tidal volume plus the expiratory reserve volume.