The density of air, ρ (Greek: rho) (air density), is the mass per unit volume of Earth's atmosphere, and is a useful value in aeronautics and other sciences. Air density decreases with increasing altitude, as does air pressure. It also changes with variation in temperature or humidity. At sea level and at 15 °C, air has a density of approximately 1.225 kg/m3 (0.0023769 slugs/ft3) according to ISA (International Standard Atmosphere).
Temperature and pressure
The density of dry air can be calculated using the ideal gas law, expressed as a function of temperature and pressure:
:
\rho = \fr...