Question: how do i know what my lean body mass is?
Answer: Men: Lean body mass = (0.32810 × W) + (0.33929 × H) − 29.5336.
For women: Lean body mass = (0.29569 × W) + (0.41813 × H) − 43.2933.
Note: 1lb = 0.453592kg, and 1in = 2.54cm.
You can also go the easy route and use an online calculator like this one here.