Here' s a test you can try.

Stand in front of a large mirror, facing it. Assume your normal shooting stance. Bring the bow up and draw straight back, slowly. When you get close to your face, watch your string hand elbow in the mirror. Don' t move your face out of your normal shooting position, just track it with your eyes. If your draw length is too short when you hit the stops, your elbow will be sticking out to the side. When your elbow comes in line with the string and arrow, you will be close to your true draw length. If your elbow comes in behind your head, your draw length is too long.

Not only is this a pretty fair test for draw length, it' s also a good test to find out if you' re overbowed. If you can' t draw the bow holding it straight out, slowly and under full control, then you' re pulling too much weight.