Lean Body Mass Calculator

How much of my weight is lean mass and how much is fat?

Get an estimate of your body’s lean mass by entering your height and weight. This calculator uses the James formula which applies to adults and children of all ages. Your lean body mass is the sum of all your nonfat parts including muscle, tissue, organs, blood, and water. Don’t confuse lean body mass with ideal weight – essential fat is 10% for women and 2% for men, and acceptable fat is up to 31% for women and 25% for men.

Field Help

Input Fields

Title: A title for these calculator results that will help you identify it if you have printed out several versions of the calculator.

US/Metric: Choose US or Metric units.

Gender: Select your gender.

Weight: Your current scale weight.

Height: Your height. Use feet (ft) and inches (in) if units is US or centimeters (cm) if units is Metric.

Output Fields

Lean Mass: The portion of your weight that is lean (not fat).

Fat Mass: The portion of your weight that is fat.

23 thoughts on “Lean Body Mass Calculator”

  1. How off can readings be when one is PMSing during their cycle ? My weigh challenge always falls the week of the above stated things, and I wonder how much it would throw my numbers off?

  2. Hi, Im from the philippines. Im 30, and i started working out last April to July, I stopped and usually go to the gym once a week since 3rd week of October up to now. Im 5’7 in height and is 72.5 kg or 160 pounds. Am i obese? How many pounds do i need to loose as to be normal or healthy. My muscles are developed already from being fat. But i wanted to me more muscular and fit. My problem is my stomach fats… Do ineed to take protein like lean mass 2000 of twinlab. Is it safe to take or not,although im working out. I wish I could have your answer ……. regards…

    • Hello Aldine, first off you are not obese.
      I can only give you advice, what you do with it is completely up to you. If you only want to lose fat you don’t need any protein powder, but if you want to gain muscle mass I would recommend whey protein. You can check out the site gnc and sort by popularity to find what will work for you. You should also go to the gym at least 3 to 4 times a week and WORK. I know so many people that go to the gym stay in there for an hour or more and barely break a sweat. I want you to drop sweat by the time your done, and don’t stop because it hurts. Only stop if it’s joint pain or an injury. And to answer your question as to how much fat you need to lose to be healthy and fit, you first need to look at what healthy and fit means.

      Eating what you are supposed to eat ACCORDING TO YOUR GOALS, will benefit you way more than any workouts will. Your diet, some would argue is 90% of being fit.

      I want you to run through some tests. Go on a run, you should get extremely out of breath to the point where you need to stop. If you hit that point at half a mile in 5 minutes you are extremely unfit. If you hit that point at a mile- a mile in a half in 10-15 minutes you are unfit. If you hit that point after two miles in 20-25 minutes you are fit.

      It’s not all about the weight. You need to look at yourself inside and out. You should look into vascular health and your BMI if you can. You’ll need to set up appointments for your BMI, but you can tell your vascular health from the description I already gave you.

      I hope this helps, I know it’s quite long but if reading this has helped in anyway I have done my job.

      Remember, break down health into goals made by you, for you. Nobody can answer the bigger questions but yourself.

  3. I agree that this calc is way off. I am 5’6″, 207lb. I agree that I am overweight, but it says that I have more body fat and less lean mass than I actually do due to my weight. It says that I have 120lb of lean mass when in actuality I have about 140+lb of lean mass due to a history of weight lifting, high bone mass and just plain genes. I have almost as much bone mass as my husband and I am 33. But it was fun seeing how I would be if I had the average body type for my weight…

  4. This is bull crap! It says that I weight 18 pounds of fatand only 94 pounds of muscle that means that I’m 16% fat but I only weigh 5 pounds

  5. This is so stupid and such a lie it says that I’m 16% fat and have 18 pounds of fat but I said that I only weigh 5 pounds and it doesn’t count for water or bones or anything for weight.

  6. According to my height, I am 40 lbs overweight. I have been working out for a little over a month now. I can see that my body is getting in shape, but for some reason my weight remains the same. I don’t see even a lb difference(220 lbs). I am 26 and I have been 175 lbs 4 years ago. So my bone weight has never been heavy. Do you think this is a medical problem or is it really turning in to muscles?

  7. Something is wrong somewhere with this calculation. In September I weighed 190 and my body fat was 48%, I started running and walking and working out. I lost some weight, but not much, but I got toned. I just got on my scale, which is the same scale that I used back in September, and it said that my body fat is 31%, the acceptable percentage, but my weight is 185. Your calculator doesn’t take into account that muscular people can be heavy and still bring down that fat percentage number. After all, doesn’t muscle weigh more than fat? Please explain.

  8. Why is it that fat people always “have more muscle mass” or “dense bones” or “genetics” that makes these estimates wrong. Bottom line… this thing isn’t even close to perfect, its just a general estimate. But, if your BMI is over 27ish, unless you are a true weight lifter (see fitness pics) you are overweight. fat, so stop whining about this calculator and loose weight.

  9. There is something fundamentally wrong with the fat to lean ratio. According to this calculator I would never be below 28% bodyfat, even if I went from 168 lbs down to 89 lbs, based on my height of 5’11” Why does the calculator assume bodyfat percentage is nearly static? People will DIE trying to use this calculator to reduce their bodyfat.

  10. im 12 and apparently the bmi i have is not normal. its 25.65 and im not obese i know that. i workout regualrly and im curious is it bad that i have a bmi like that when im 138 lbs and im 5.1 in a half?

  11. If an athlete or other person with a lot of muscle has a BMI over 25, is that person still considered to be overweight?

    According to the BMI weight status categories, anyone with a BMI between 25 and 29.9 would be classified as overweight and anyone with a BMI over 30 would be classified as having obesity.

    However, athletes may have a high BMI because of increased muscularity rather than increased body fatness. In general, a person who has a high BMI is likely to have body fatness and would be considered to be overweight or obese, but this may not apply to athletes. A trained healthcare provider should perform appropriate health assessments to evaluate an individual’s health status and risks.


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