Vital capacity is the maximum amount of air a person can expel from the lungs after a maximum inspiration. It is equal to the inspiratory reserve volume plus the tidal volume plus the expiratory reserve volume.

A person's vital capacity can be measured by a spirometer which can be a wet or regular spirometer

Spirometry

Spirometry is the most common of the pulmonary function tests , measuring lung function, specifically the measurement of the amount and/or speed of air that can be inhaled and exhaled...

. In combination with other physiological measurements, the vital capacity can help make a diagnosis of underlying lung disease. The unit that is used to determine this vital capacity is the millilitre (ml).

A normal adult has a vital capacity between 3 and 5 litres. Predicted normal values for VC can be calculated online and depend on age, sex, height, weight and ethnicity as well as the research study that they are based upon.