In both respects it’s much more than one might think. At any one time, we are wrapped in 4.99 million million tons of it – that is 4.99 followed by 13 zeros. It varies of course with the heat and the pressure, but at sea level, and at the ordinary temperature of a summer day, one cubic meter of air weighs about 1.14 kilograms. It produces at sea level a pressure of about 6.66 kilograms per square inch. This means that upon the skin of medium-sized person there is a constant total pressure of 13,590 kg., but it is transmitted equally in every direction. The person is not crushed, because he is like an inflated toy balloon with enormous pressure outside but an equally strong pressure inside. So, there is little strain on the delicate elastic tissue.
It is estimated that for all practical purposes the atmosphere terminates at nearly 100 kilometers above the sea level. However, a few air molecules linger here and there for a few kilometers more, until more or less total vacuum of space begins.