Mike Horne, age 11, of Bessemer City, North Carolina, for his question:

How much air does a person need a day?

We measure air capacity by the cubic foot. This is the amount required to fill a square box measuring one foot on all sides. In an average day, an average man breathes in and breathes out about 400 cubic feet of ordinary air. This would fill a small room ten feet long, five feet wide and eight feet high. People who do strenuous exercise need more than average and everybody breathes at a slower rate while sleeping.

This seems like a lot of air to breathe into our lungs and out again every day of our lives. But the lungs are interested only in its oxygen content. During an average 24 hour day, an average man needs to absorb about 20 cubic feet of oxygen. Not all the oxygen is removed from the air we breathe. Most of it is breathed out again with our waste carbon dioxide and the other unused gases of the air