If your draw length is 30 inches, how long should the arrow be? Also if you put a string loop on how much shorter would your draw length need to be?

It depends on rest, loop, etc. I am a 30" draw, use a loop and have used 28" , but now run 27.5" CX300' s. You can goto a proshop and they will be able to test what arrow length you need with a draw arrow for your setup. Also can determine for you what spine or type arrow will be the best for that setup and arrow length.

Hope this helps

knock an arrow, draw your bow, mark the arrow about an inch forward of the rest cut and reassemble the arrow then go hunting after you retune your bow.
have the bow shop put a string loop on and they will adj your draw lenght. your draw lenght really depends on what kind of release you are useing and how big of loop they put on.

i have a 30" draw and have my arrows cut to 28.5 but could go to 28 with a nap qt4000