Mixing Ratio of Air Calculator
Find the water vapor mixing ratio of air.
Mixing ratio is the mass of water vapor per kilogram of dry air.
How the Math Works
The water vapor mixing ratio, denoted as w, is calculated using the formula w = 0.622·e ÷ (P - e). In this equation, e represents the water vapor pressure in hectopascals (hPa), and P is the total atmospheric pressure, also in hPa. The constant 0.622 derives from the ratio of the gas constants for water vapor and dry air (Rv/Rd). This formula determines the mass of water vapor per unit mass of dry air, providing a dimensionless quantity that quantifies humidity independent of temperature.
Practical Applications
To use this calculator, measure or obtain the water vapor pressure (e) using a hygrometer or psychrometer, and the total atmospheric pressure (P) from a barometer or local weather data. Input these values into the formula to determine the mixing ratio. Meteorologists and HVAC engineers use this calculation to assess atmospheric conditions for weather forecasting, aircraft performance calculations, and designing efficient heating, ventilation, and air conditioning systems to maintain optimal indoor humidity levels.
Day-to-Day Use
Understanding the water vapor mixing ratio helps you interpret weather forecasts more accurately, as it indicates the actual amount of moisture in the air rather than just relative humidity percentages. This knowledge assists in daily decisions like choosing appropriate clothing for the day, predicting whether outdoor activities might be affected by fog or precipitation, and managing indoor comfort by adjusting humidifiers or dehumidifiers to maintain healthy humidity levels for your home and health.
Worked example
25 °C, 60% RH, 1013 hPa → about 11.9 g/kg.
FAQ
Mixing ratio vs specific humidity?
Mixing ratio uses dry-air mass; specific humidity uses total moist-air mass.