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Categories: General Health

Lean Body Mass (LBM): Definition & Formula

By Marc Perry / February 20, 2016

Question of the Week: What Is Lean Body Mass?

I’ve been getting a lot of questions recently about “Lean Body Mass”, so I thought it would be a good idea to address the concept in more depth so you can understand exactly what it is, why it’s important, and how to calculate it.

Definition: What is Lean Body Mass (aka LBM)?

Simply put, lean body mass is comprised of everything in your body besides body fat.1 Your lean body mass includes:

…and anything else in our bodies that has mass and is not fat.

As an aside, for the average adult male about 42% of body weight is skeletal muscle and it’s about 35% for females.

Lean Body Mass Formula:

Lean Body Mass = Body Weight – (Body Weight x Body Fat %)

This equation is taking your body weight in pounds and subtracting it from the amount of fat you have in your body in terms of pounds.  Simple.  If you don’t know how to measure your body fat, here are 5 Ways to Measure Body Fat.

Beware of some of the calculators online that attempt to arrive at your lean body mass without knowing your body fat percentage first.  These calculators attempt to calculate your lean body mass based on your height, weight, age, and/or sex, which will most likely be completely inaccurate.

Why Is Knowing Your Lean Body Mass Important?

Most people rely 100% on the weight scale when attempting to track changes in body fat.  While I do strongly recommend Monday Morning Weigh Ins during a fat loss program (and even after) as a proxy for fat loss, tracking body fat directly and tracking LBM is helpful to make sure you are losing only fat and no muscle.  Losing muscle is highly undesirable because your metabolism will decrease and aesthetically, you may not look leaner even if you do lose weight.

Lean body mass is also your set point to determine how much fat you should lose and what your body fat percentage will be if you lose a certain amount of fat.  You can check out the Ideal Body Weight Formula, which takes into account your lean body mass to arrive at your ideal weight.

If you would like to learn more about losing fat without losing muscle, I highly recommend checking out my free Get Lean Guide.

I hope this was helpful.  Let me know if you have any questions, or have anything to add by leaving a comment.

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43 Comments

  • kathie says:

    Hi Marc
    I see all kinds of information about bodyfat%, but so far have been unable to find any indication of what a healthy lbm weight would be for my height. the reason this is important to me is that I am trying to figure out whether i just need to shed some more fat and accept my lbm as it is, or build up more muscle.
    my lbm on my tanita fluctuates from around 46kg to 49kg (101-108lb)and I am 176cm 5'9.5"tall
    two years ago I successfully shed around 18kgs (40lbs) and my lbm stayed pretty much the same, so I lost purely fat. However my bf is still too high, although my weight is ok. Do you think my goal should be to build more muscle? or just shed more weight/fat. Or if you could direct me to any sites that talk about lbm or have lmb charts that would be fantastic. Thanks!

    • Marc Perry, CSCS, CPT says:

      @kathie - over the years, I've done body fat assessments on many women and I can tell you that somewhere around 110lb would be more ideal for a women your height. With that said, 100lb is still a solid level. I would say anything underneath that level would be too little. This is just from my experience and LBM is a little tricky because some people have bigger and heavier bones than others. The other thing you can do is measure your body parts like your legs, arms, waist and see what they are. For example, if your thighs are much less than 19 inches, that's pretty thin. Finally, you could even think of your LBM in terms of strength. I plan on creating an awesome post that will show the various body fat percentages, weight, and measurements of various men and women. I plan on doing this in the next three months, so if you haven't signed up on our email list yet, I would do that: http://www.builtlean.com/email/. Sorry I could not give you something more specific, but non of this is an exact science.

      • Abhisaar says:

        HI marc...i am skinny guy and my weight is 45 and i workout gym last year and 2-3mnths ago i took whey gold standard protein and now i took lean body mass 60 and is it good for me without any cause of problem? Please help marc...thank you!

        • Marc Perry, CSCS, CPT says:

          @Abhisaar - I would check out this article on Whey Protein. In my opinion, protein supplements are 100% not necessary to get you the results you want, they can however be convenient for some people are have trouble eating enough protein from whole food sources.

  • kathie says:

    First of all Marc, Thanks so much for taking the time to respond to me personally. I have pretty big legs from doing a lot of cycling. they are 20". However my Tanita segment scale tells me that (strangely) one of my legs is overfat. I think its my left.

    But seriously, my plan now is going to be to get my lbm up to over 110 on a continuous basis (the tanita goes up and down, but it does show trends) and at the same time I'm going to drop another 3kgs of fat in the coming months. I'm looking forward to reading your newsletter. BTW, i posted a similar question on the facebook page of cutthefatpodcast and got a completely different answer to the one I was looking for, but certainly really interesting.

    I guess in the end its all about building strength so that you can do other stuff and not simply for the sake of having a certaing lbm.

    Thanks again!
    Kathie

  • Abhisaar says:

    Dear marc..i agree ur commentd but i eat whole food and everything cuz i am pure veggie not non-veg as i cant egg too...i eat sandwich,cheese,vegetables,milk and many more as i was 42kgs and now almost 45.5kgs :) and i workout hard so need to drink protein shake after workout to gain weight and muscle gain...so took lean body mass 60 as trainer said and spoke to doctor also before i take this protein he said i can have it....:) so wad u think marc and can you tell me is dat okay or if not then plz tell me..i wuld really thank you for ur help...wich is good protein shake for me after workout to gain muscle and weight and protein shake i cant drink egg u knw :)...thank! Waiting for ur reply

    • Marc Perry, CSCS, CPT says:

      @Abhisaar - We don't have any articles on protein shakes at this time, but you can check out this article on Whey Protein, which has some whey protein recommendations.

  • Moo says:

    Hi Marc. I am female, 5.6, 288 pounds, 40.9 body fat (on two scales). My lean body mass sounds too much? I use to be 120. Does the water count in it? I am always dehydrated. And how to know that I'm losing body fat? If my lean body mass doesn't change that's good, right? Thanks.

    • Marc Perry, CSCS, CPT says:

      @Moo - Because your body fat is relatively high, it's a lot more difficult to measure and track lean body mass. If I were you, I wouldn't track LBM, I would track your weight instead as a proxy for fat loss. As long as you are doing some resistance training and eating ample protein, let's say 100 grams per day, you shouldn't lose any muscle. In addition, those who have more fat to lose will generally lose little muscle on larger calorie deficits because your body will readily use body fat stores.

  • Alvin says:

    I've been lifting weights for two years consistently now. I'm 240 lbs. with 20-22% body fat. If I were to drop 20 pounds of purely fat, would it be possible to do it without losing any muscle that I've built? Or does losing that kind of weight always correlate with at least some muscle loss at the expense of time ("the faster you lose fat the more you'll lose muscle - idea"). I've taken a nutrition class and understand how macros and caloric deficits work. Thank you for your time.

    • Marc Perry, CSCS, CPT says:

      @Alvin - That's a great question. From my own experience with my training clients, I never had one client lose an ounce of muscle while losing fat (well actually one who tried a very low carb diet when he was already lean). This is because they did intense strength training, did not go too low on the calorie deficit, and ate sufficient protein (roughly 0.8grams per pound of body weight). I think if you follow these 3 guidelines, you can keep the vast majority of your muscle mass. As you start getting around 10-12% body fat, it's very possible that you lose a little muscle mass. So let's say a bodybuilder looking to get shredded for competition may lose 3-5lb of muscle as he strips his body of all the fat he can.

  • Lisa says:

    Hi
    Why is it that calculating lean body mass and ideal body fat ratios using your guide generally results in target weight lower than other recommended guides? Should height be considered and age? Thanks

    • Marc Perry, CSCS, CPT says:

      @Lisa- WHat "other recommended guides" are you using? For example, I weight 170lb and I'm 5'11''. According to the BMI Index for my height, a "normal" weight range would be from 133 to 179 pounds. Also, keep in mind the ideal body weight formula is individual specific. A better barometer of over health may be the waist to height ratio, which is a relatively new metric that research has shown may be better than the BMI Index.

      Best,
      Marc

  • Ashraff says:

    hi, i have weight around 110kg's..is it recommended to drink the weight body mass product because i exercise almost everyday and intending to build up my muscle and loosing fat..please help me,im clueless

    • Marc Perry, CSCS, CPT says:

      @Ashraff - I highly suggest signing up for our weekly newsletter and reading over the Get Lean Guide.

  • Harpreet says:

    Sir i have lost 40 kg in 1.5 years , have i also lost my lean body mass ? I am now at 65 kg and height 5 feet 7 inches

    • Kristin says:

      Hi Harpreet,

      Any time you lose weight, you also lose some lean muscle. The way to maintain muscle while losing fat is to perform full-body strength workouts 3-4x per week. If you don't currently strength train, I would recommend adding that to your current workout program. Congrats on your weight loss thus far! Keep up the good work!

      -Kristin, BuiltLean Coach & Managing Editor

  • Angelica says:

    Hello, my lean body mass is 94.6. Can you tell me what that means?

    • Kristin says:

      Hi Angelica,

      Your lean body mass is your total body weight minus your current body fat. So you have 94.6 lbs of fat-free mass. Using your lean body mass, you can determine the amount of body fat you currently have (Total Body Weight - Lean Body Mass = Total Body Fat). To calculate your body fat percentage, divide your body fat by your total weight (Body Fat / Total Weight = Body Fat percentage).

      -Kristin, BuiltLean Coach & Managing Editor

  • Anita says:

    Hi, interesting to read all of these comments. My weight has fluctuated between 50.7 kg to 51.3 kg; I'm currently 51 kg. I'm 5'2.5" tall. My body fat percentage goes up when I lose weight. I train 3x week CF. 51 years old. I don't understand why my body fat increases if I;m losing weight. Currently 24.7% body fat. I eat healthy I thought. I would like to get my body fat down and leaner athletic body. Don't want to lose the weight - how do you get a balance?

    • Kristin says:

      Great question, Anita. It's not easy to answer without knowing about your eating and exercise routine. Decreasing your calories and solely doing steady state cardio doesn't help you maintain (or build) lean muscle while you're losing weight. In this scenario, you're likely to lose both fat and muscle, which could cause you to have a higher body fat percentage. If you're not currently doing strength training, then I definitely recommend adding weights to your training program. While you're focused on losing weight, strength training helps you retain lean muscle mass while primarily losing body fat. Aim for 2-3 days of strength training per week.

      If you're interested in following a workout and nutrition program than helps you lose weight while getting lean & strong, then you should check out the BuiltLean Transformation program. Have more questions? Feel free to reach out to us at support@builtlean.com. Hope that helps!

      -Kristin, BuiltLean Coach & Managing Editor