Kathryn, lean body mass is not the same as your goal weight. LBM refers to your body weight minus all fat. You have to have a certain % of fat in order to live. For women it is generally accepted that 18% is the lowest level of body fat for optimal health - below that certain biological functions cease. Guidelines change based on age - the older you get the higher the range that is considered optimal.

With a LBM of 115 lbs and 20% BF you would weigh 138 lbs.

To get your LBM in Kgs divide it by 2.2.

Nat