Most bow manufacturers will recommend or warranty no less than so many grains per pound of draw weight. For instance, my Switchback is no less than 5 grains per pound. I'm drawing 70lbs, so my total arrow weight should be no less than 350 grains.

Figure out the weight of your nock, vanes, bh or field pts, and insert and subtract that number from the recommended total arrow weight and you will have the minimum bare arrow weight. Divide the recommended min bare arrow weight by the length and you will have the recommended min. grains per inch. This will obviously give you the most speed w/o potentially damaging your bow, but it may not give you the most kinetic energy.
hope that helps