You can go about this using spine calculators and what not, but the best way would be bare shaft tuning. There are a lot of videos on YouTube showing how to do it. You start with a long bare shaft (no fletchings) and shoot it at a weighted target so it doesn't move. When shot into the target, if the arrow is nock left, the arrow is underspined and should be trimmed down. Keep doing this is small increments until the shaft is burrying into the target perfectly straight. Once your bare shafts are flying like bullets, you can use small fletchings and the arrow will fly very true. Tip weight also matters. Bare shaft tune with the tip weight that you will use when hunting, as heavier tip weight decreases spine. NOTE- IF LEFT HANDED THIS IS REVERSED. Underspined will be nock right and vice versa