Calculate moist atmospheric air density, dew point, and density altitude from temperature, barometric pressure, elevation, and humidity.
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The Air Density Calculator calculates the density of atmospheric air by applying the ideal gas law for moist air (CIPM / ISA formulations). Because humid air contains water vapor (molecular mass 18 g/mol) that displaces dry air (diatomic nitrogen and oxygen, average molecular mass 29 g/mol), moist air is actually lighter and less dense than dry air.
\rho = \frac{p_d}{R_d \cdot T} + \frac{p_v}{R_v \cdot T}Where p_d is partial pressure of dry air, p_v is partial pressure of water vapor, R_d is specific gas constant for dry air (287.058 J/(kg*K)), R_v is for water vapor (461.495 J/(kg*K)), and T is absolute temperature in Kelvin.
Scenario: Standard International Standard Atmosphere (ISA) sea level conditions: 15°C, 1013.25 hPa, 0% humidity.
T = 15 + 273.15 = 288.15 K.
p = 101,325 Pa, pv = 0.
Density: 101,325 / (287.058 × 288.15) = 1.2250 kg/m³.
Counter-intuitively, humid air is lighter and less dense than dry air. Water vapor molecules (H2O, 18 g/mol) displace heavier nitrogen (N2, 28 g/mol) and oxygen (O2, 32 g/mol) gas molecules.
Under the International Standard Atmosphere (ISA) definition at 15°C (59°F) and 1013.25 hPa (29.92 inHg), air density is exactly 1.225 kg/m³ (0.07651 lbs/ft³).
Air density drops exponentially with elevation. At 2,000 meters (~6,560 ft), air density is roughly 80% of sea level; at 5,000 meters (~16,400 ft), it is only 60%.
Density altitude is pressure altitude corrected for non-standard temperature. It represents the altitude at which the current air density would occur in a standard atmosphere.
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