Vapour Pressure Calculation Enter a temperature or a dewpoint or both: If you want the saturated vapor pressure enter the air temperature: saturated vapor pressure: Fahrenheit Celsius Kelvin mb in of HG mm HG hPA kPA lbs per square in If you want the actual vapor pressure enter the dewpoint: actual vapor pressure: Fahrenheit Celsius Kelvin mb in of HG mm HG hPA kPA lbs per square in If you enter both the air temperature and the dewpoint you'll get a bonus answer. relative humidity - requires both temp and dewpoint %