T Nation

Calculating Lean Body Mass


I know this may be a stupid question but I wasn't sure. Is the calculation
for lean body mass as simple as:

Total body weight -
(Total Body fat % X Total body weight) = Lean Body Mass?

For ex.

(200 lbs) - (.12 X 200) = LBM?

How do you calculate lean body mass?
Is the above right?



Long reply, ain't it?


Yes, that is correct. A 200lb man with 10% bodyfat would have 180 lbs of "lean body mass" and 20lb of fat mass.

However, I would like to point out that "lean body mass" isn't really the correct phrase. "lean" is really supposed to mean muscle, but obviously not all of that 180lbs would be muscle. Therefore, "lean body mass" is a bit of a misnomer. It really should be fat-free-mass. It's not really critical to quibble over it, but there is a distinction. Because basically, if you go from 200lb at 10% bodyfat to 210lb at 9.5%, that means you put on 10lb of lean body mass. But you would have 190lb of fat-free-mass and 20lb of fat-mass. In some equations for calculating calories via BMR or some such it is important to know fat-free-mass, fat mass, and an estimate for lean-body-mass since muscle tissue, fat tissue, and organs/everything else - each have different metabolic rates, so it helps to know the mass of each to be able to calculate more accurately.

So basically, you are calculating correctly. But don't tell someone you have 180lb of "muscle". You have 180lb of fat-free-mass. And 20lb of fat. However changes in weight can be stated in fat-mass and lean-mass/muscle. So you could gain 20lb of muscle and 5lb of fat, you wouldn't say you gained 20lb of fat-free-mass and 5lb of fat unless you went through puberty and grew taller or gave yourself an extra liver or something.


Thanks for the replies