Humidity Mixing Ratio Calculator

About this calculator

The water vapor mixing ratio (w) expresses humidity as the mass of water vapor carried per unit mass of completely dry air, calculated from vapor pressure (e) and total atmospheric pressure (p) with the formula w = 0.622 × e ÷ (p − e), where 0.622 is the ratio of the molar masses of water and dry air. Unlike relative humidity, which depends on temperature, the mixing ratio stays constant for a parcel of air as it moves and changes temperature, as long as no moisture is added or removed, which makes it a conserved quantity meteorologists prefer for tracking air masses.

Meteorologists use the mixing ratio on thermodynamic diagrams like the Skew-T log-P chart to analyze atmospheric moisture profiles and forecast precipitation, while HVAC and industrial-drying engineers use the closely related concept in psychrometric calculations to size dehumidification and ventilation equipment.

Enter the vapor pressure and total air pressure and this calculator returns the mixing ratio, typically expressed in grams of water vapor per kilogram of dry air.