A model of how atmospheric pressure varies with altitude:

Standard conditions for temperature and pressure

Atmospheric models

The International Standard Atmosphere (ISA), an international standard model, defining typical atmospheric properties with altitude, at mid-latitude.

Atmosphere (unit), an approximation of the value at sea level

The U.S. Standard Atmosphere, a series of models that give values for pressure, density, and temperature over a range of altitudes

NRLMSISE-00 is an empirical, global model of the Earth's atmosphere from ground to space. It models the temperatures and densities of the atmosphere's components. A primary use of this model is to aid predictions of satellite orbital decay due to...