Ketoviante -: There is going to be a little math here, but hold on and we will get through it. Your lean weight is the first calculation we will need to make. This won't be your total body weight of course. Let's take an example of someone weighing 200 pounds. If you now tip the scales at 200 with, let's say, 20% body fat, then, your lean body mass weight will be 160 pounds.