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.

19 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…

  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?


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