# Actual Vapor Pressure

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Actual vapor pressure, abbreviated as e, is the measurement to the amount of water vapor that is in a volume of air. As the volume of air increases, the volume of water vapor increases.  The actual vapor pressure is the measurement as to how moist the air is.  Relative humidity (RH) is defined as the ratio of the water vapor density to the saturation water vapor density and is expressed as a percent.

 $$\large{ e = \frac { RH \; e_s } { 100 } }$$ Where: $$\large{ e }$$ = actual vapor pressure $$\large{ RH }$$ = relative humidity $$\large{ e_s }$$ = saturated vapor pressure