Draw your bow to your normal anchor point and have someone put a small pencil mark on the arrow at the front of the arrow shelf. Measure the arrow to that mark and it's your draw length...WITH THAT BOW. Each bow, depending on the length of the arrow shelf and depth of the throat on the grip, will measure differently.
There used to be a term called "True Draw," coined by Tom Jennings, I think, that measured draw length from the throat of the grip. Of course, draw length measured that way is much shorter, but it's consistent bow to bow, except for the difference due to high, medium, or low wrist hold.