Absolute Humidity and Mixing Ratio Calculator
Convert relative humidity and temperature into absolute moisture content: grams of water per cubic metre, mixing ratio and vapour pressure.
- es = 6.112 × exp(17.62 T ÷ (243.12 + T)) = 31.6 hPa
- e = RH × es = 18.96 hPa
- AH = 216.7 × e ÷ T(K) = 13.78 g/m³
Humidity Formulas
AH = 216.7 × e ÷ (T + 273.15) g/m³
x = 622 × e ÷ (p − e) g/kg
e is the actual vapour pressure (RH × es) and p the total pressure in hPa. The Magnus coefficients give good accuracy from about −45 to 60 °C.
Worked example
Air at 25 °C and 60 % RH has a vapour pressure of 19.0 hPa, an absolute humidity of 13.8 g/m³ and a mixing ratio of 11.9 g/kg.
Frequently Asked Questions
What is the difference between relative and absolute humidity?
Relative humidity is the percentage of the maximum vapour the air could hold at that temperature; absolute humidity is the actual mass of water per volume of air.
What is mixing ratio?
The mass of water vapour per kilogram of dry air, used in HVAC and drying calculations.
Why does heating air lower its RH?
Warmer air can hold more water, so the same moisture content becomes a smaller fraction of saturation.
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