Welcome to the site, and more importantly......Welcome to the trade!
I don't want to scare you away but as for formula's our trade uses, well you might wanna sit down grab a pen & paper and read some of the guys posts on this site. They will teach you alot.
Currently I'm in my final term of Trade school and in this level (Advanced) I have aquired the knowlage of at least 12 new formulas for many things including sizing motor pulleys, Velocity, CFM conversions, heatloss, static pressure and many more.
My best avice to you is take the time and get into trade school. It has helped me, and now I'm looking to wrte my licence within the next month.
until then here is a few formula's for you to investigte:
1) BTUH = CFM x 1.08 x TD
------- = CFM
TD x 1.14
Maybe if you find out what these mean (do a little investigating) and find it interesting, I can post a couple questions and teach you what is going on.