Dew Point Calculator

The dew point is the temperature air has to be cooled to before water vapour starts condensing out of it, which is why it tracks how muggy a day feels better than relative humidity does. Enter the air temperature and the relative humidity in Celsius or Fahrenheit and you get the dew point, how far it sits below the air temperature and the vapour pressure behind it. A second mode goes backwards and returns relative humidity from a measured dew point. The arithmetic uses the Magnus formula with the Alduchov and Eskridge coefficients, which are fitted for air between -40 C and 50 C, so temperatures outside that band are refused rather than extrapolated.