At about 11 inches long and nearly 6 inches wide, the lungs together weigh only about two pounds. They contain about 1 1/2 gallons of air.

The inside of your lungs is covered with 300 to 600 million tissue-thin sacks called alveoli. Stretched out flat, the alveoli would cover a tennis court.

Each day, the average adult inhales about 4,250 gallons of air, containing about 40 billion trillion molecules of oxygen. Along with it comes about 20 billion particles of dirt and other foreign matter.

When you cough, the air rushing out of your lungs hits speeds of 75 to 100 miles per hour.