The
density of air, ρ (Greek: rho) (air density), is the mass per unit volume of
Earth's atmosphere. Air density, like air pressure, decreases with increasing altitude. 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 (0.001225 g/cm
3, 0.0023769
slug/ft
3, 0.0765
lbm/ft
3) according to ISA (
International Standard Atmosphere).