Here is a link for free ET_AEE software that performs calculations for you.
Psychrometry is the study of moist air. The psychrometric chart displays the relationship between dry-bulb, wet-bulb, and dew point temperatures, and specific and relative humidity. Given any two, the others can be calculated. To use the chart, take the point of intersection of the lines of any two known factors (interpolate if necessary). and then from that intersection point, follow the lines of the unknown factors to their numbered scales to obtain the corresponding values.