I would really like to know the formula for this, but I was reading through shape magazine and they were advertisiting their exercise and diet site and said it had a free 10 day trial. Since Shape has quite a few good exercises they post in their magazine, I wanted to see what their website would have.
Anyway, I went to www.ishape.com
and before you officially sign up (pretend you are signing up) there is this buttom that says "Body Fat Calculator" where depending on your height, weight and measurements, it will give you a pretty good estimate on your body fat percentage. The lean body mass it gave me was pretty damn close to what mine was when I got it officially done. Of course it says I have a BF % of 44% which isn't the best but it is better than where I was before.