The average adult male's lungs can hold a maximum of 6 liters (about 1.5 gallons) of air, according to the American Lung Association. This includes air from a normal breath, plus extra air you can force in, additional air you force out after a regular exhalation, and any air left in the lungs after all that. The association estimates that you consume 2,000 gallons (7,570 liters) of air per day.
The air that is inhaled is about 20 percent oxygen, and the air that is exhaled is about 15 percent oxygen, so about 5 percent of the volume of air is consumed in each breath and converted to carbon dioxide. Therefore, a human being uses about 100 gallons (378 liters) of pure oxygen per day (5 percent of 2,000 gallons).
A person who is exercising obviously uses a lot more oxygen than that. You could determine how much air is moving through your lungs by exhaling into a plastic bag of known volume at each breath and seeing how long it takes to fill the bag.