Let’s let the Moose explain this one.

Lean body weight or mass,  a waste of arithmetic

Talking Moose
Talking Moose
Whoever wrote that headline, likes bluntness.


Sometimes, people ask me to explain what is "lean body weight".  It’s not what you think.  It has nothing to do with your ideal weight, or what your body should be like if you were "lean".

Talking Moose
Talking Moose
Do people actually ask you questions like that?

Dr. Halls Dr. Halls
Not for a long time actually, I can’t remember the last time.

Talking Moose
Talking Moose
Praise be, to wikipedia and google.


Lean body mass,  refers to the sum of the weight of your bones, muscles and organs… basically the sum of everything other than fat in your body.

But who would like to have a body with ZERO fat?  Nobody.  In fact, you’d probably die if you had no fat.

Talking Moose
Talking Moose
There’s a nursery rhyme about Jack Sprat, could eat no fat… The modern version: Jack and his wife try a bunch of diets and write a blog.


So why is it included along with BMI on the body surface area calculator page?  Because it’s kind of fun to think about,  thats all.  

Talking Moose
Talking Moose
Building a play fort in the kitchen, is also fun.


Also, some medical formulas use lean body mass for various calculations of organ function and medication doses.

Maybe you are wondering why your lean body mass goes up,  as your weight goes up,  even though your height is unchanged. 

Hector Hector
No. I wasn’t wondering that. Where am I?


The reason is that the skeletal muscle mass tends to increase as body fat increases.  It takes extra muscle to carry extra fat around, right?

Hope this helps.

The formula for lean body mass using the method of James1,2 is:

Lean Body Weight (men) = (1.10 x Weight(kg)) – 128 x ( Weight2/(100 x Height(m))2)
Lean Body Weight (women) = (1.07 x Weight(kg)) – 148 x ( Weight2/(100 x Height(m))2)

An alternate formula for lean body mass using the method of Hume3 is

For men over the age of 16: lean body mass in kilograms = (0.32810 * (body weight in kilograms)) + (0.33929 * (height in centimeters)) – 29.5336

For women over the age of 30: lean body mass in kilograms = (0.29569 * (body weight in kilograms)) + (0.41813 * (height in centimeters)) – 43.2933

David David
Dammit. Two formulas. My OCD makes me wonder, which is better and are they in the correct order?


These formulas are trusted and highly scientific, based on various types of measurements of human body composition, including dual energy X-ray absorptiometry (DEXA). However, remember that they are based on "averages". They predict the lean body weight "average" of a group of people with similar height and weight.

But you, as an individual, might have more muscle than others in your group, or bigger internal organs, or denser bones, or any number of factors that make you a little different than others. So even the lean body weight formulas are estimates.


  1. Hallynck TH Soep HH et al. Should clearance be normalised to body surface or to lean body mass? Br J Clin Pharmacol. 1981; 11: 523-526.
  2. James WPT. Research on obesity. London. Her Majesty’s Stationery Office.
  3. Hume R. Prediction of lean body mass from height and weight. J Clin Path. 1966; 19

Dr. Halls Dr. Halls
The above references were from the original page in 1999. I’ve updated in 2014 and found a few more references below.

Talking Moose
Talking Moose
MooseFingerLeftAlso, there’s a Lean body mass calculator on the body surface area page.


  1. Mettler S, Mitchell N, Increased protein intake reduces lean body mass during weight loss in athletes. Med Sci Sports Exerc, 2010; 42:326-37.
  2. Volek JS, Volk BM, et al. Whey protein supplementation during resistance training augments lean body mass. J Am Coll Nutr. 2013; 32:122-35.

Did you click on any faces or find other surprises?


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