Rule of Thumb when changing belts!??

HI guys...my ac belt busted and now my alternator belt on my D16a is looking REALLy bad. I don't have a torque wrench or a tension bar....what is the basis on how you know when a belt is too tight? Just by examining it by hand, how can you tell? I heard that if you can turn it only half way then its ok....if you can turn it more then its too loose, and if you cant turn it half way then its too tight...

any pointers??

Thanks

JesseCrx