how does a person know what arrow size they would need in a wood shaft

With wood arrows it goes by spine. Stiffness of the arrow.

Magnus

oxtail call up a reputable supplier and tell them you and your bow spec's. They can send you a test kit of 3-4 different spines in your range. Shoot them all until you find the spine that shoot's great. I spent too much money and too much time experimenting when I could have spent 30 bucks on a test kit and been done with it.

I would suggest that you contact Paul Jalon at Elite Arrows, a sponsor on here. He can set you straight. Check out Elite Arrows on the Sponsor Listing.

A lot of variables when choosing the proper shaft in any material.

thanks a ton fellas

Try this formula:
Draw weight +5 lbs.
Cut to center  +5
every inch over 28" +5/inch
125 gr-145 gr points +0
FF string +5

It should get you in the ballpark.  Or try Stu's calculator.