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Mixing Ratio of Air Calculator
Calculate the mixing ratio of moist air — the mass of water vapor per unit mass of dry air — from vapor pressure and total pressure.
hPa
hPa
What mixing ratio is
The mixing ratio of moist air is the mass of water vapor contained in a given mass of dry air. It’s a key quantity in meteorology and HVAC psychrometrics for describing atmospheric humidity.
The formula
Mixing ratio w = ε × e / (P – e), where e is the partial pressure of water vapor, P is the total atmospheric pressure, and ε = 0.622 is the ratio of the molecular weight of water to that of dry air. The result is typically expressed in grams of water vapor per kilogram of dry air.
This is the standard meteorological formula for mixing ratio, used for general educational and reference purposes.
Last reviewed August 2026