The length of your arrow depends on your draw length. Go to an archery shop and have them measure your draw length when at full draw with your bow, and then they can set you up with the arrow of proper length, diameter, grain weight, and stiffness according to your draw weight (how many pounds you are pulling) and what you'll be hunting. For elk, probably a 60-70 pound draw with pretty heavy arrows. I shoot a 600 grain arrow at 70 pounds. Arrow goes at about 247 feet per second with a 125 grain broadhead and 4 inch fletching. Plenty of zip and lots of weight to punch through an elk. Good luck and let us know how you do BMF