1. What is the volume of Earth's atmosphere?
The "effective volume" of the Earth's
atmosphere is about 4.2 billion cubic
kilometers. This figure is the surface area of the
Earth (509 million square kilometers) times the
"effective thickness" of the atmosphere (8.2
kilometers, or about 27,000 ft). The effective
thickness and volume are what the thickness
and volume of the atmosphere would be if the
entire atmosphere were at sea level conditions.
The actual volume of the atmosphere is
considerably greater than its effective volume,

2. The actual volume of the atmosphere is
considerably greater than its effective volume,
as its pressure and density drop with increasing
altitude. If we adopt the "Karman Limit" of 100
km elevation as the boundary between earth
and space, the volume of the atmosphere
would be 100 times 509 million or about 51
billion cubic kilometers. However, the Karman
Limit is a non-physical and rather arbitrary
boundary.