肺活量为用力吸气后尽力呼出的气体总量，能够反映一次呼吸时的最大通气能力。它是潮气量（平时自由呼吸时一次所呼出的气量）、补吸气量（最大吸气时的增量）和补呼气量（最大呼气时的增量）三者的总和。其正常值为成人男子为3500毫升、女子2500毫升，有过专业训练的运动员可以达到8000毫升以上。肺活量反映了肺通气功能和身体机能状况，其意义在于以下几点：

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

A person's vital capacity can be measured by a wet or regular spirometer. In combination with other physiological measurements, the vital capacity can help make a diagnosis of underlying lung disease. Furthermore, the vital capacity is used to determine the severity of respiratory muscle involvement in neuromuscular disease, and can guide treatment decisions in Guillain-Barré syndrome and myasthenic crisis.