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, 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.