I'm going to guess around .500 but you didn't say your draw length, or if is cut to center. 3Rivers Archery has a pretty easy to use (and free) arrow calculator. I think Stu helped design it. It'll allow you to get a baseline of different options. It will get you very close and your form and other personal factors associated with the bow and the shooter can be fine tuned with slight tip weight changes, strike plate build-out, and brace height. Just an option. You're likely to get several different answers.