Felting...How to?

So I mentioned that I was going to felt myself a tea cozy using my 1 Fish, 2 fish charts. Right? I know very little about designing felted projects but I am willing to learn..off a researching I will go! I googled 'designing felted projects'. WOW! there is a wealth of people selling their felted projects. But what I was really after was how big you should knit something before you felt it down. That info was a little harder to find. But I found it! Knitted to felted pieces generally shrink 20-25% width wise and between 40-50% lengthwise Depending on the type of wool used. Everybody strongly suggests swatching. Man. I hate swatching. But I guess I will do so. I think I have decided to use worsted weight Wool of the Andes Now I have to ponder the amount of yarn to order for this project...