You are absolutely correct where BMI (Body Mass Index) is not as accurate as something like BIA:
Description
BIA stands for Bio-Electric Impedance Analysis. It is a simple and inevasive way to get your body composition analyzed. Body composition is the ratio of fat mass to fat free mass in your body. This is a much better indicator of your health than scale weight. 2 electrodes are stuck on your hand, and 2 on your feet, and a very small electrical current is passed through your body. The more fat one has, the slower the current. Fat acts as an insulator in the body.
Based on BMI standards at 5'5", 190 lbs, my body fat would be 31.6% which places me in the OBESE category. But, when I take the BIA body assessment, my body fat index is measured at 19.4%, which obviously accounts for my greater than average muscle mass. 12%-18% is the goal I am trying to reach to be in the 'fit' category, but at least I now know I am considered to be at a 'normal' weight for my body composition instead of 'OBESE'. If you want the most accurate assesment, I know the method where they submerse your body is the most accurate but it is hard to find places that do it. The next best thing is the eletro resistance method which is much cheaper as well.
Here is the site for Ryerson University for those in Toronto that are interested in the procedure:
http://www.firefly.ryerson.ca/sportsandrec/index.cfm?page=recreation/training/programs/bia