Air pressures at various sea levels

The atmosphere is about 50 miles "deep," and at sea level it exerts 14.7 psi. That is, a 1-inch-square column of air 50 miles high weighs 14.7 pounds. Our bodies think 14.7 psi of air pressure is completely normal.

Sea level - 14.7 psi
10,000 feet - 10.2 psi
20,000 feet - 6.4 psi
30,000 feet - 4.3 psi
40,000 feet - 2.7 psi
50,000 feet - 1.6 psi