Pocket Metrologist™

Humidity Calculator

Calculate between humidity values at different temperatures and pressures. Convert between %RH, dew point, frost point, PPMV, PPMW, and vapor pressure. Optionally displays WMO humidity and enhancement factors. Performs calculations for a two temperature, two pressure humidity generatior.


Most users will only need the Basic calculator. To change between calculators, touch the spinner at the top and select the desired calculator. To change any value, click on the number box then enter the new value. After changing any value, other values will be automatically calculated.

The system temperature and pressure are inputs only and are more important than you might think. For a given amount of water in the air %RH changes with both pressure and temperature changes! Set these both when calculating %RH and set the pressure when calculating dew/frost point.

The rest of the variables (except enhancement factors which are hidden by default) are both inputs and outputs. When you set one parameter (for instance "Dew Point") then all of the other parameters in this section are recalculated. When you change temperature or pressure, the most recent entry in the in/out section stays the same.

By clicking the menu key, then "Options" you can change the units for pressure and temperature. You can also change between wet and dry ratios. For instance the wet volume ratio is the volume of water divided by the total gas volume. The dry volume ratio is the volume of water divided by the volume of other gasses.

The Math

Coming Soon

Home Page | Software | Webmaster | ©2012 Matthew Vernon | Updated: January 28, 2012