Knowledge of the psychrometric properties is essential during the designing of air conditioning, cold storage, and drying processes where humid air is a working fluid. In this study detailed procedures for calculating psychrometric properties are given. Seven main properties of the psychrometrics, namely dry-bulb, wet-bulb and dew-point temperatures, atmospheric pressure, humidity ratio, relative humidity and enthalpy can be calculated using the given procedures. According to the Gibbs Phase Rule, in the humid air case, any three intensive properties will be sufficient to evaluate the remaining properties. Therefore the combination of three out of seven properties gives a total of 35 different sets. Computer software has been developed and utilised to obtain the psychrometric properties of humid air. It was found that given three input parameters, the remaining four parameters could, except in three cases, can be calculated with negligible error.