The only way to know for sure is to draw a bow that has the same/similar grip and draw weight. I've tried all the "tricks" I have ever seen to guesstimate draw length without a bow (including the yard stick) and none of them work for me. I figure they will work for some, but don't bet the house on it.

I'll third the fact that as you develop your form and shooting muscles your draw length will change.

Chad