(a) Inspiratory Reserve volume (IRV) is an additional volume of air a person can inspire by a forcible inspiration. It averages 2500 ml to 3000 ml. Expiratory Reserve volume (ERV) is an additional volume of air that a person can expire by a forcible expiration. This averages 1000 ml to 1100 ml.

(b) Inspiratory capacity (IC) is the total volume of air a person can inspire after a normal expiration. It is the sum of tidal volume and inspiratory reserve volume. Expiratory capacity (EC) is the total volume of air a person can expire after a normal inspiration. It is the sum of tidal volume and expiratory reserve volume.

(c) Vital capacity is the maximum volume of air a person can breathe in after a forced expiration. It is the sum of Tidal volume, expiratory reserve volume and inspiratory reserve volume. It is also the maximum volume of air a person can breathe out after a forced inspiration.

Total lung capacity is the total volume of air accommodated in the lungs at the end of a forced inspiration. It is the sum of Residual volume, expiratory reserve volume, tidal volume and the inspiratory reserve volume.