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Browse all calculatorsEnter sex, weight and height to compare three published formulas side by side, or type a measured body fat percent. Metric and US units.
The equations come from published papers: Boer (1984), James (1976) and Hume (1966). Age is only an adult check, because none of the three uses it. Sources are listed below the calculator.
This is a general estimate for educational use. It is not medical advice, a diagnosis or a treatment plan. Talk to a doctor, registered dietitian or other qualified professional before you change your diet, exercise or health care.
| Formula | Lean mass | Lean share | Fat mass |
|---|
Private by design. Everything runs in your browser and is never uploaded.
Lean body mass is the part of your body weight that is not fat: muscle, bone, organs, blood, skin and body water. A lean body mass calculator estimates it from sex, height and weight with the Boer, James or Hume formula, or subtracts fat mass when you type a measured body fat percent.
This lean body mass calculator shows all three formulas side by side, then fat mass and the lean share of your weight, so you can see how far apart published equations land. Results change as you type and the working shows every step. If you do not know your body fat percent, the body fat calculator can estimate one from measurements. Every figure here is an estimate, not a measurement.
| Person | Boer | James | Hume |
|---|---|---|---|
| Woman, 165 cm, 65 kg | 46.1 kg (101.7 lb) | 46.6 kg (102.7 lb) | 44.9 kg (99.0 lb) |
| Man, 180 cm, 80 kg | 61.4 kg (135.4 lb) | 62.7 kg (138.3 lb) | 57.8 kg (127.4 lb) |
| Man, 5 ft 10 in, 160 lb | 57.8 kg (127.5 lb) | 58.5 kg (129.0 lb) | 54.6 kg (120.4 lb) |
| Weight and body fat | Lean body mass | Fat mass |
|---|---|---|
| 80 kg at 20% body fat | 64.0 kg (141.1 lb) | 16.0 kg (35.3 lb) |
| 65 kg at 30% body fat | 45.5 kg (100.3 lb) | 19.5 kg (43.0 lb) |
| 100 kg at 25% body fat | 75.0 kg (165.3 lb) | 25.0 kg (55.1 lb) |
The first answer is already on screen. Change any number and it updates at once, with no Calculate button.
Choose metric (kg and cm) or US (lb, feet and inches). The published equations have one version for men and one for women, so pick the version you want to compare.
Commas and units such as 65 kg are fine. Age must be 18 to 100 and is only an adult check, because none of the three formulas uses age.
If a scan or other test gave you a body fat percent, type it. The result then also shows lean mass as weight × (1 − body fat ÷ 100).
Compare the three rows in the table, tap a name to show it in the big result, then copy the summary or share a link that opens with the same numbers.
W is weight in kilograms and H is height in centimetres. Every calculation runs in kg and cm. US entries are converted first with pounds × 0.45359237 and inches × 2.54, and lean mass in pounds is kilograms × 2.20462.
Fat mass is weight minus lean mass, and the lean share is lean mass ÷ weight × 100. Numbers are rounded half up to one decimal place for display only; the calculation keeps full precision. The coefficients below match two open-access papers that print all three equations (see the sources).
| Formula | Men | Women |
|---|---|---|
| Boer (1984) | 0.407 W + 0.267 H − 19.2 | 0.252 W + 0.473 H − 48.3 |
| James (1976) | 1.1 W − 128 (W ÷ H)² | 1.07 W − 148 (W ÷ H)² |
| Hume (1966) | 0.32810 W + 0.33929 H − 29.5336 | 0.29569 W + 0.41813 H − 43.2933 |
| Measured body fat | W × (1 − body fat % ÷ 100), same for everyone | |
Each equation is a curve fitted to a different group of people, so each carries that group with it. Four things move the answers apart.
Hume used 56 adults aged 37 to 80. Boer used 87 adults aged 19 to 72. The 2022 comparison paper notes that most such equations came from small samples, mostly of white populations.
Hume worked out lean mass from total body water. Boer presented estimated lean mass as an index for scaling blood and fluid volumes. The 2022 comparison used DXA scans, a different method from either.
Boer and Hume are straight lines in weight and height. James subtracts a squared weight-to-height term, so it bends as weight rises and stops rising near a BMI of 43 for men and 36 for women.
No formula uses age, muscle, training or body shape. Two people with the same sex, height and weight get the same answer.
| Formula | Built from | Shape | Worth knowing |
|---|---|---|---|
| Boer | 47 men aged 21 to 72 and 40 women aged 19 to 68 | Straight line in W and H | Published to scale blood and fluid volumes |
| James | DHSS/MRC obesity report, 1976, later used in drug research | Weight minus a (W ÷ H)² term | Falls as weight rises past BMI 43 (men) or 36 (women) |
| Hume | 29 men aged 40 to 77 and 27 women aged 37 to 80, lean mass from body water | Straight line in W and H | Smallest and oldest sample. Correlation 0.96 for men, 0.83 for women |
A 2022 study compared such equations with DXA scans of 1,558 UK adults aged 60 to 65. The differences from the scan for 95 percent of people fell within a band about 13 kg wide for Boer, 14 kg for James and 17 kg for Hume, and the authors found two other equations closer. DXA is itself not a perfect reference. Treat the three results as a range rather than a single truth.
Lean body mass in kilograms when the body fat percent comes from a measurement, worked out as weight × (1 − body fat ÷ 100) and rounded to one decimal.
| Body weight | 10% | 15% | 20% | 25% | 30% | 35% | 40% |
|---|---|---|---|---|---|---|---|
| 50 kg (110.2 lb) | 45.0 | 42.5 | 40.0 | 37.5 | 35.0 | 32.5 | 30.0 |
| 55 kg (121.3 lb) | 49.5 | 46.8 | 44.0 | 41.3 | 38.5 | 35.8 | 33.0 |
| 60 kg (132.3 lb) | 54.0 | 51.0 | 48.0 | 45.0 | 42.0 | 39.0 | 36.0 |
| 65 kg (143.3 lb) | 58.5 | 55.3 | 52.0 | 48.8 | 45.5 | 42.3 | 39.0 |
| 70 kg (154.3 lb) | 63.0 | 59.5 | 56.0 | 52.5 | 49.0 | 45.5 | 42.0 |
| 75 kg (165.3 lb) | 67.5 | 63.8 | 60.0 | 56.3 | 52.5 | 48.8 | 45.0 |
| 80 kg (176.4 lb) | 72.0 | 68.0 | 64.0 | 60.0 | 56.0 | 52.0 | 48.0 |
| 90 kg (198.4 lb) | 81.0 | 76.5 | 72.0 | 67.5 | 63.0 | 58.5 | 54.0 |
| 100 kg (220.5 lb) | 90.0 | 85.0 | 80.0 | 75.0 | 70.0 | 65.0 | 60.0 |
| 110 kg (242.5 lb) | 99.0 | 93.5 | 88.0 | 82.5 | 77.0 | 71.5 | 66.0 |
| 120 kg (264.6 lb) | 108.0 | 102.0 | 96.0 | 90.0 | 84.0 | 78.0 | 72.0 |
Many lean body mass calculators give one number from one formula. These are the details that change how far you can trust a result.
| Feature | Basic calculator | This calculator |
|---|---|---|
| Formulas | One at a time, or three with no explanation | Boer, James and Hume side by side, plus a body fat route, with the reasons they differ |
| Results | Calculate button or page reload | Updates as you type, with an answer on first load |
| Outputs | Lean mass and a percentage | Lean mass, fat mass and lean share in kg and lb, plus the spread between formulas |
| Working | Answer only | Unit conversions, each formula with your numbers, and the rounding rule |
| Age | Often no adult check, or a child option | Adults 18 to 100 only; younger ages get a plain note instead of a result |
| Warnings | Rarely flagged | Caps a result at body weight, flags the James peak and heights and weights outside the Hume sample |
| Sources | Author and year at best | Papers, coefficients, sample sizes and a DXA comparison cited |
| Sharing | Rare | Copy the summary or share a link with the same numbers |
See how far Boer, James and Hume land from one another for the same height and weight, and read the spread as a range.
Type a percent from a scan or a skinfold test to see lean mass and fat mass in kg or lb. To get a percent from tape measurements, try the body fat calculator or the Army body fat calculator.
Compare the lean mass on a body composition printout with an estimate, keeping in mind that lean body mass and fat-free mass are sometimes used as one term.
Physiology, nutrition and health students can check a hand calculation against the working shown under the result.
Copy the summary into the online notepad or share a link so the same numbers open later.
Some clinical papers scale doses or fluid volumes to lean mass. This page is not for medication dosing, but it shows what the equations in those papers produce. Another size measure used in medicine is body surface area, on the body surface area calculator.
This page does not tell anyone what their lean body mass should be. A doctor or other qualified professional can say what a figure means for you.
Lean body mass includes bone, organs, blood, skin and water, so it is always larger than muscle mass alone.
Many sources use the two terms as one. Behnke, who proposed lean body mass in 1942, counted a little essential fat in it, and a 2024 review argues both have the same chemical composition. Check which term a report uses.
Formulas only use sex, height and weight. Scans such as DXA, or other body composition tests, measure the body directly, with their own error.
When you type a body fat percent, the answer is exactly as good as that measurement. Different test types give different percentages for the same person.
Reference sources commonly quote about 60 to 90 percent of body weight as lean mass, varying with sex, age, build and fitness.
Nothing you type leaves your browser. A shared link carries your numbers in the page address, so only share it with people you choose.
The formulas are for adults. Ages 18 to 100 are accepted, and anyone younger sees a note to ask a doctor or school nurse instead of a result.
It gives an estimate for education, not medical advice, a diagnosis, a treatment plan or a medication dose. Questions about your own health are best taken to a doctor or other qualified professional.
A formula can give more than your body weight at unusual heights and weights. The result is then capped at your weight and a note says so. Weights run from 25 to 400 kg and heights from 100 to 250 cm.
Every coefficient is printed in the two open-access papers below, which list all three equations. The 1976 James and Waterlow report is a printed government publication that could not be opened, so its numbers rest on those papers.
Short answers about lean body mass, the three formulas and their limits.
Lean body mass is your total body weight minus fat mass. It counts muscle, bone, organs, blood, skin and body water, and is usually given in kilograms or pounds or as a share of body weight.
Use a formula based on sex, height and weight, or subtract fat mass when you know a body fat percent. The Boer formula for a woman is 0.252 × weight in kg + 0.473 × height in cm − 48.3, and the body fat route is weight × (1 − body fat ÷ 100).
Multiply your weight by 1 minus the body fat percent divided by 100. At 80 kg and 20 percent body fat, lean body mass is 80 × 0.80 = 64.0 kg and fat mass is 16.0 kg. The result is only as accurate as the body fat measurement behind it.
They are three published equations that estimate lean body mass from height and weight, with separate versions for men and women. Hume (1966) and Boer (1984) are linear in weight and height, while James (1976) subtracts a term based on the squared weight-to-height ratio.
They were built from different groups of people, measured in different ways, and the James formula bends differently from the other two as weight rises. For a 65 kg, 165 cm woman they give 46.1, 46.6 and 44.9 kg, so a gap of a kilogram or two is normal.
No single one is best for everyone, and none replaces a scan. In a 2022 comparison with DXA scans of 1,558 UK adults aged 60 to 65, 95 percent of the differences fell within a band about 13 kg wide for Boer, 14 kg for James and 17 kg for Hume, and the authors found two other equations closer. Treat the three results as a range.
Reference sources commonly give about 60 to 90 percent of body weight, and the share depends on sex, age, build and fitness. This calculator shows your own share for each formula, and a doctor can say what a figure means for you.
Many sources use the terms interchangeably. Behnke, who proposed lean body mass in 1942, counted a small amount of essential fat in it, while fat-free mass is defined as everything except fat, and a 2024 review argues the two have the same chemical composition. Check which term a report uses before comparing numbers.
No. Lean body mass also includes bone, organs, blood, skin and water, so it is larger than muscle mass alone. None of the three formulas can tell how much of a result is muscle.
No. The formulas are for adults, so the calculator accepts ages 18 to 100 and shows a plain note for anyone younger. Questions about growth or body composition in children and teenagers are best taken to a doctor or school nurse.
Some clinical papers scale doses or fluid volumes to lean mass, but this page is not for medication dosing. Doses are set by a prescriber or pharmacist who knows the full clinical picture.
No. The calculation runs in your browser and nothing is sent to a server. Your numbers appear in the page address only so a shared link opens with the same values, and your choice of metric or US units is remembered on your own device.