How to measure your arrow length?
Place the rear end of your necked shaft on your chest bone under your chin and reach out both of your hands for the other end of the shaft. Your sufficient arrow length is there where your middle finger touches the shaft. Ask someone to mark it down with a visible pen mark.
You'll find the right arrow length by lifting your arms up after placing the nock end on top of your chest bone. The point where your middle finger touches the arrow shaft is the right cutting length.