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Lean Body Mass Calculator

Find out how much of your body weight is lean mass. Enter your weight and body-fat percentage for a direct calculation, or estimate lean mass from your height and weight.

Formula shown on the pageMetric, US and UK unitsNo sign-up, no data stored

Your details

Sample values. Change them to yours.
Method
%
Not sure of your body fat? Estimate it with a tape measure, or choose Height & weight.

Your details stay in this browser. Nothing you enter is sent to a server.

Estimated lean body mass
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Fat mass
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Lean share of weight
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Resting calories (Katch-McArdle)

How it was worked out:

A body-fat result is only as accurate as the percentage you enter. A height-and-weight estimate is based on population averages and does not measure your body composition.

How your body fat % changes the result

Same weight, different body fat estimates. Your entry is highlighted.

Body fatLean mass

Use your lean mass next

These open with the values you entered. Anything you did not enter, such as age or activity, appears there as a sample value to change.

Katch-McArdle calculatorResting calories and TDEE from your lean mass. TDEE calculatorYour daily calories and a goal target. FFMI calculatorYour lean mass relative to your height.
Written by Updated Sources listed at the end

What is lean body mass?

Lean body mass is your body weight minus your fat. It includes muscle, bone, organs, blood, skin and the water in all of them. Muscle is only one part of it, so lean mass is not a measure of how muscular you are on its own. This calculator estimates lean mass from the numbers you enter; it does not measure your body.

Scientists use related terms in slightly different ways. Strictly, the "weight minus all fat" figure this calculator gives is called fat-free mass, while some researchers define lean body mass to include a small amount of essential fat. In everyday use, and on this page, the two mean the same thing. Because lean mass is mostly water, your hydration on the day can shift any estimate.

How to use the lean body mass calculator

If you know your body-fat percentage

  1. Choose Body fat %. It is selected by default.
  2. Enter your weight in kilograms, pounds or stone, and your body-fat percentage.
  3. Read your lean mass and fat mass. The table under the result shows how much the answer moves if your body fat estimate is a few points off.

If you do not know your body-fat percentage

  1. Choose Height & weight.
  2. Select your sex and enter your height and weight.
  3. Read the estimate, and remember it is based on population averages. For a personal number, estimate your body fat with a tape measure and switch back to the first method.

How to calculate lean body mass

Formula using body-fat percentage

Fat mass = weight × body fat % ÷ 100
Lean body mass = weight × (1 − body fat % ÷ 100)

Weight can be in any unit; the answer comes out in the same unit. Body fat is a percentage, such as 20.

Example calculation

80 kg at 20% body fatFat mass = 80 × 20 ÷ 100 = 16 kg. Lean body mass = 80 × (1 − 0.20) = 64 kg. If the true body fat were 25% instead, lean mass would be 60 kg, which shows how much the result depends on the percentage you enter.
200 lb at 25% body fatFat mass = 50 lb. Lean body mass = 200 × 0.75 = 150 lb.

Formula without body-fat percentage

When you do not know your body fat, the calculator uses the Boer equation, published in 1984. It needs weight in kilograms and height in centimetres; the calculator converts pounds, stone and feet for you.

Men: lean mass (kg) = 0.407 × weight + 0.267 × height − 19.2
Women: lean mass (kg) = 0.252 × weight + 0.473 × height − 48.3
A man, 178 cm and 80 kg0.407 × 80 + 0.267 × 178 − 19.2 = 32.6 + 47.5 − 19.2 = 60.9 kg, which implies about 24% body fat.

Boer built the equation from relatively small groups of adults, and it predicts what is typical for someone of your height and weight, not what you actually carry. Other equations, such as Hume (1966) and James, give different answers for the same person, and the James formula can produce impossible results at high body weights. No single equation is best for everyone. If an equation ever gives a lean mass of zero or more than your total weight, the calculator shows a warning instead of a number.

What does your lean body mass result mean?

Lean mass is a weight, not a health score. It depends mostly on your height, frame and sex, so there is no universal ideal. A 190 cm man and a 160 cm woman can both be lean and healthy with lean masses 30 kg apart.

Lean mass versus body-fat percentage

Body-fat percentage tells you what share of your weight is fat; lean mass tells you how many kilograms are everything else. They move together: at a fixed weight, a higher body fat means a lower lean mass. During a diet, if your weight falls while your estimated lean mass holds steady, that suggests most of the loss is fat, provided you measured body fat the same way each time.

Lean mass versus muscle mass

Muscle mass is only part of lean mass. Bone, organs and water make up the rest, and this calculator does not measure any of them: it works from the numbers you enter. A rise in estimated lean mass over months of strength training can reflect added muscle, but it can also come from water, glycogen or measurement error, so check it against your strength, your waist and how your clothes fit.

How accurate are lean body mass calculators?

The arithmetic is exact; the inputs are not. With the body fat method, any error in your body fat estimate carries straight into the result: at 80 kg, each 1 point of body fat changes lean mass by 0.8 kg. With the height-and-weight method, the result reflects averages from the people the equation was built on, so it can be far off for very muscular people, very lean people and people with obesity. Use the result as an estimate, compare it over time using the same method, and be wary of any calculator that promises a precise accuracy figure.

How to estimate your body-fat percentage

  • Tape-measure equations, such as the US Navy method in our body fat calculator, use your waist, neck and (for women) hips. They are free and repeatable, but assume a typical fat distribution.
  • Bioimpedance scales send a small current through your body. Readings change with hydration, recent meals and exercise, so measure at the same time each day.
  • Skinfold callipers depend heavily on the skill of the person measuring.
  • DXA scans use low-dose X-rays to estimate fat, lean tissue and bone mass in different parts of the body. They are among the most detailed methods available, but they cost money and results still vary between machines and with hydration.

Each method has its own assumptions. Pick one you can repeat, and use it every time, so changes reflect your body rather than the method. See what a DEXA scan costs if you are considering one.

How to use lean body mass for calories and fitness

Estimate resting calories with Katch-McArdle

BMR (calories a day) = 370 + 21.6 × lean body mass in kg

At 64 kg of lean mass: 370 + 21.6 × 64 = about 1,752 calories a day. That is your basal metabolic rate, the energy you use at rest, not your total daily needs, and any error in your lean mass carries into it. Add your activity with the Katch-McArdle calculator or the TDEE calculator, and compare formulas in the BMR calculator.

Track body composition

Recalculate every 4 weeks or so, using the same method in similar conditions: same time of day, same scale, before eating. Look at the trend over two or three readings rather than any single change, since water alone can move lean mass by a kilogram or more.

Understand FFMI

Fat-free mass index divides your lean mass by your height squared, so you can compare yourself with people of other heights. Find yours with the FFMI calculator, and read whether you can build muscle in a calorie deficit if you are trying to keep lean mass while losing fat.

Related

Body fat calculatorGet the body fat number this calculator needs.Katch-McArdle calculatorCalories from lean mass.FFMI calculatorLean mass for your height.

Sources

  1. Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol. 1984;247(4 Pt 2):F632–F636. PubMed 6496691
  2. Hume R. Prediction of lean body mass from height and weight. J Clin Pathol. 1966;19(4):389–391. PubMed 5929341
  3. Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men from body circumferences and height. Report No. 84-11. San Diego, CA: Naval Health Research Center; 1984.

Frequently asked questions

How do I calculate lean body mass?
Multiply your weight by one minus your body fat percentage as a decimal. At 80 kg and 20% body fat: 80 × (1 − 0.20) = 64 kg of lean mass. The other 16 kg is fat mass.
Can I calculate lean body mass without knowing my body fat?
Yes. Height-and-weight equations such as Boer (1984) give a population-based estimate. They do not measure your body composition, so two people with the same height and weight get the same answer even if one is far more muscular. For a personal number, estimate your body fat first with the body fat calculator.
Is lean body mass the same as muscle mass?
No. Lean body mass includes muscle, bone, organs, blood, skin and body water. Muscle is only one part of it, so your lean mass is always much larger than your muscle mass.
What is lean body weight?
Lean body weight is a term commonly used for your body weight excluding fat, the same idea as lean body mass. Medicine and research use slightly different definitions, so read how a source defines it before comparing numbers.
What is a good lean body mass?
There is no single ideal number. Lean mass depends mostly on your height, frame and sex, so a tall man naturally carries far more than a short woman. To compare yourself with others of your height, use the FFMI calculator; to track yourself, watch your own trend.
Can lean body mass change without gaining muscle?
Yes. Water, glycogen and the food in your gut all count as lean mass, so hydration, a high-carb day or a salty meal can move the number. Measurement error in your body fat estimate also changes the result.
Can I use lean body mass to calculate calories?
Yes, as a starting point. The Katch-McArdle equation estimates resting calories as 370 + 21.6 × lean mass in kg. That is your BMR, not your daily total: add activity with the TDEE calculator.
How often should I calculate my lean body mass?
Every 4 weeks is plenty. Use the same method, at the same time of day and in similar conditions, and compare the trend over months rather than single readings.