Saturation vapor density

Saturation vapor density (SVD) is a concept closely tied with saturation vapor pressure. It is useful for getting an exact quantity of water vapor in the air from a relative humidity (RH). Given an RH percentage, the density of water in the air is given by RH * SVD = Actual Vapor Density. Alternatively, RH can be found by RH = Actual Vapor Density / SVD. As Relative Humidity is a percent, vapor density can be in whatever units are necessary, usually grams or kilograms per cubic meter.

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For low temperatures (below 400 kelvins or so), SVD can be approximated from the SVP by the ideal gas law: PV = nRT where n is the number of moles, which is related by density by n = M/m, where M is the mass of water present and m is the molar mass of water (18.01528 grams/mole). Thus, setting V to 1 cubic meter, we get P*m/(R*T) = M/V = density.

R is the Boltzmann constant, and T is the temperature in kelvins.