So basically you want to find out how much lean body mass you have.
You can buy a specialized weight scale that tells you what you're body fat percentage is...but it is not very accurate http://kyleleon2.plebu.com/
The best thing to do is go to someone who knows how to measure body fat with a caliper...most doctors and fitness trainers know how to perform this. Then you will be able to tell how much excess fat you have http://customizedfatloss.nation2.com/