Moisture Holding Capacity of Air table or function? It is strange but I cannot find the good table of Moisture Holding Capacity of Air g/kg or lb/lb like the chart here:
https://www.engineeringtoolbox.com/moisture-holding-capacity-air-d_281.html

I am trying to make calculations in MS Excel visual basic module, I have the absolute humidity and need to get the relative humidity for given temperature.
 A: The maximum amount of water that air can hold is given by the Antoine equation for water.  For a given temperature, when the partial pressure of water vapor in air is equal to its vapor pressure, the air is at 100% humidity.  Note that the calculation will normally be on a molar basis, so there is a conversion involved if you want to convert to kg water vapor per kg of dry air.
For more information on the Antoine equation, see https://en.wikipedia.org/wiki/Antoine_equation
A: If A is the absolute humidity(in mass of water vapor per mass of dry air), the moles of water vapor per mole of dry air is $$m=\frac{29}{18}A$$The mole fraction of water vapor in the in the air is $$x=\frac{m}{(m+1)}=\frac{29A}{29A+18}$$If $p_{atm}$ is the current atmospheric pressure, then the partial pressure of water vapor in the air is $$p=xp_{atm}=\frac{29A}{29A+18}p_{atm}$$The relative humidity is the partial pressure divided by the equilibrium vapor pressure of water vapor at the temperature T ($p_{vap,eq}$) times 100 %:$$RH=100\left(\frac{29A}{29A+18}\right)\frac{p_{atm}}{p_{vap,eq}}$$
A: tables of functions like these are available in any textbook dealing with the discipline of heating/ventilating/air conditioning (a.k.a. "HVAC") engineering. 
A: This page offers 
a pair of formulas of "Empirical fit of saturated vapor density versus Celsius Temperature". For T in 0..40°C you can use 5.02 + 0.323*T + 8.18e-3*T^2 + 3.12e-4*T^3, where T is measured in Celcius (this is an approximation and I've eliminated significant digits that have no visible effect on a high-resolution chart.)
