The formulations used here to calculate moist air properties are based on perfect gas relations published in 1989 ASHRAE Fundamentals Handbook, which should be accurate enough in majority of air-conditioning problem. Nevertheless, I strongly recommend you to compare the results calculated by this worksheet with a psychrometric chart. There is limited error checking so you should use reasonable input values. Don't hesitate to let me know if you find any bugs.

Worth to know?
If you search for the key word "psychrometric calculator" using either Googles or YAHOO search engine, you will find this page at the top of the search list. It is no surpeise of course since YAHOO uses Googles search engine. You can also try the button "I'm Feeling Lucky" at Googles and it brings you right back here. Using Altavista on the other hand, this page comes as number 2 hit on the search list. (Too bad for Altavista!!)
I would also like to thank all of you for your positive response/e-mails.