The average adult at rest inhales and exhales something like 7 or 8 liters (about one-fourth of a cubic foot) of air per minute. That totals something like 11,000 liters of air (388 cubic feet) in a 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 550 liters of pure oxygen (19 cubic feet) per day.
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.
Here are some interesting links:
- How Your Lungs Work
- If water is made up of hydrogen and oxygen, why can't we breathe underwater?
- Is it harmful to breathe 100-percent oxygen?
- How Exercise Works