Respiratory Volume

During normal quiet breathing, about 500 ml of air moves into and then out of the lungs with each breath. This respiratory volume is the tidal volume (TV). 

The amount of air that can be inspired forcibly beyond the tidal volume (2100 to 3200 ml) is the inspiratory reserve volume (IRV). 

The expiratory reserve volume (ERV) is the amount of air— normally 1000 to 1200 ml—that can be expelled from the lungs after a normal tidal volume expiration.

Even after the most strenuous expiration, about 1200 ml of air remains in the lungs; this is the residual volume (RV), which helps to keep the alveoli patent (open) and prevent lung collapse.