Air Density Calculator
Air density depends on temperature, atmospheric pressure, and humidity. Warmer air is less dense, higher pressure compresses air to higher density, and surprisingly, humid air is lighter than dry air because water vapor (molecular weight 18) replaces heavier nitrogen (28) and oxygen (32) molecules. This calculator uses the ideal gas law with humidity correction to give you accurate results.
The calculation combines Dalton's law of partial pressures with the ideal gas law:
rho = pd/(Rd x T) + pv/(Rv x T)
Where pd is the partial pressure of dry air, pv is the vapor pressure, Rd = 287.058 J/(kg·K) is the specific gas constant for dry air, Rv = 461.495 J/(kg·K) is the specific gas constant for water vapor, and T is absolute temperature in Kelvin.
Standard sea-level air density is 1.225 kg/m³ at 15°C, 1013.25 hPa, and 0% humidity (ISA standard atmosphere).
Air density matters in many fields:
- Aviation: Lower air density reduces lift and engine power, increasing takeoff distance
- Ballistics: Drag on a bullet depends directly on air density
- Wind energy: Power output is proportional to air density (P = 0.5 x rho x A x v³)
- HVAC: Fan performance and duct sizing depend on air density
- Sports: A baseball travels farther in thin (warm, high-altitude) air