Lung volumes and lung capacities refer to the volume of air associated with different phases of the respiratory cycle. Lung Volumes are directly measured; lung capacities are inferred from lung volumes. The average total lung capacity of an adult human male is about 6 litres of air, but only a small amount of this capacity is used during normal breathing.

Tidal breathing is normal, resting breathing; the tidal volume is the volume of air that is inhaled or exhaled in only a single such breath. The average human respiratory rate is 30-60 breaths per minute at birth, decreasing to 12-20 breaths per minute in adults.