At rest, the average adult inhales around 20 percent oxygen in the air and exhales about 15 percent oxygen, according to HowStuffWorks. People inhale and exhale approximately 7 or 8 liters of air each minute or 11,000 liters per day.
HowStuffWorks states that 5 percent of the volume of air is consumed each time a person inhales and is converted to carbon dioxide. Thus, a person uses around 550 liters of pure oxygen daily. Dr. Dawn A. Tamarkin of the Springfield Technical Community College explains that the normal amount of air breathed in and out at rest is called the tidal volume of air. The maximum amount of air a person can inhale and exhale is known as the vital capacity. A person normally does not use his entire vital capacity. When speaking or being active, a person takes in and lets out more air than the tidal volume.
The body only uses air when there is gas exchange, which occurs in the alveoli, notes Dr. Tamarkin. Upon inhaling, a person takes air into the respiratory system, and the air travels into the alveoli. Some air remains in the nasal cavity, trachea, bronchi and bronchioles to avoid creating a vacuum. The air stays in the respiratory passageways, and it cannot be used by the body.