Lean body mass
calculator.
Estimate how much of your weight is not fat, from your height and weight with three published formulas side by side, or directly from a body fat percentage you already know. It flags any formula that stops being valid for your build.
Estimated lean body mass is 135.6 lb by the Boer formula, 75% of your weight; James 138.5 lb and Hume 127.0 lb.
- Lean body mass, Boer (1984)
- 135.6 lb (61.5 kg)
- Range across the formulas
- 127.0 lb to 138.5 lb
- Implied fat mass (Boer)
- 44.4 lb
- Implied body fat (Boer)
- 24.7%
- BMI
- 25.8 kg/m²
W = 81.65 kg, H = 177.80 cm. Boer: 0.407 × 81.65 + 0.267 × 177.80 − 19.2 = 61.50 kg; James: 1.10 × 81.65 − 128 × (81.65 ÷ 177.80)² = 62.82 kg; Hume: 0.32810 × 81.65 + 0.33929 × 177.80 − 29.53 = 57.58 kgEverything
except the fat.
- Boer (1984): men 0.407W + 0.267H − 19.2; women 0.252W + 0.473H − 48.3. James (1976): men 1.10W − 128(W/H)²; women 1.07W − 148(W/H)². Hume (1966): men 0.32810W + 0.33929H − 29.53; women 0.29569W + 0.41813H − 43.29. W in kilograms, H in centimeters, result in kilograms.
- From a known body fat percentage: lean body mass = W × (1 − body fat ÷ 100). This needs no height or sex.
- The headline uses Boer; all three are shown with their range. James is marked not valid at a BMI of 42.97 or more for men and 36.15 or more for women, where its curve peaks and more weight would give less lean mass. Any result of zero or more than body weight is also marked not valid.
- Pounds are converted with 1 lb = 0.45359237 kg and inches with 1 in = 2.54 cm. Nothing is rounded until display, to 0.1 lb or kg.
- Adults only. For information, not medical advice: clinical uses such as drug dosing need a clinician.
How do you calculate lean body mass?
If you know your body fat percentage, subtract the fat: lean body mass = weight × (1 − body fat ÷ 100). At 200 lb and 25% body fat that is 200 × 0.75 = 150 lb, with 50 lb of fat. If you do not, estimate it from height and weight with a published formula. A man 5 ft 10 in (177.8 cm) and 180 lb (81.65 kg) gets 0.407 × 81.65 + 0.267 × 177.8 − 19.2 = 61.5 kg (135.6 lb) by the Boer formula, 75% of his weight.
LBM = W × (1 − BF ÷ 100)What are the Boer, James and Hume formulas?
All three predict lean body mass in kilograms from weight W in kilograms and height H in centimeters, with separate equations for men and women. Hume (1966) fitted them to total body water in 29 men and 27 women. James (1976) is from a UK government report on obesity research. Boer (1984) was developed to normalize body fluid volumes. For the 180 lb man above they give 61.5 kg (Boer), 62.8 kg (James) and 57.6 kg (Hume), so the spread is about 5 kg. That spread is a fair picture of how uncertain any height-and-weight estimate is.
Boer men: 0.407W + 0.267H − 19.2 women: 0.252W + 0.473H − 48.3
James men: 1.10W − 128(W/H)² women: 1.07W − 148(W/H)²
Hume men: 0.32810W + 0.33929H − 29.53 women: 0.29569W + 0.41813H − 43.29Why does the James formula fail at high BMI?
The James formula subtracts a term that grows with the square of weight, so beyond a certain point each extra kilogram lowers the predicted lean mass. Setting the slope to zero puts the peak at a BMI of 1.10 × 10,000 ÷ 256 = 42.97 for men and 1.07 × 10,000 ÷ 296 = 36.15 for women, in line with the plateau Caruso et al. (2018) describe at about 43 and 37. A woman 160 cm tall and 100 kg (BMI 39.1) gets 49.2 kg from James but 52.6 kg from Boer and 53.2 kg from Hume. The calculator marks James as not valid there and uses Boer.
What is the difference between lean body mass and fat-free mass?
Fat-free mass is strictly everything except fat. Lean body mass is often used to mean the same thing, though some authors count a small amount of essential fat in organs and bone marrow as lean. In everyday use, and in this calculator, both mean weight minus fat. A DXA scan reports fat and lean tissue directly and is far more precise for one person than any formula here.
How accurate are lean body mass formulas?
They are population averages, so one person can be several kilograms off. Puri and Blake (2022) compared ten such equations with whole-body DXA in 1,558 adults aged 60 to 65. Hume’s average bias was small (−1.1 kg), but its error changed systematically with body size. For a 40-year-old man like the one above, a body fat estimate from tape measurements in the body fat calculator gives 65.0 kg of lean mass, against 57.6 to 62.8 kg from the formulas. Use whichever estimate you can best support, and track change over time with the same method.
Worked examples.
Man, U.S. units
Man, 5 ft 10 in, 180 lb.
135.6 lb by Boer (75% of weight); James 138.5 lb, Hume 127.0 lb.
Load this exampleMan, metric
Man, 180 cm, 75 kg.
59.4 kg by Boer; James 60.3 kg, Hume 56.1 kg.
Load this exampleWoman, metric
Woman, 165 cm, 60 kg.
44.9 kg by Boer (75% of weight); James 44.6 kg, Hume 43.4 kg.
Load this examplePast the James peak
Woman, 160 cm, 100 kg (BMI 39.1).
52.6 kg by Boer and 53.2 kg by Hume; James (49.2 kg) is marked not valid at this BMI.
Load this exampleFrom a known body fat percentage
200 lb at 25% body fat (for example from a DXA scan).
150.0 lb of lean mass and 50.0 lb of fat.
Load this exampleWhat this calculator
does not do.
- The formulas are adult population equations from small samples. For one person the result can be several kilograms off, and the body fat they imply is rougher still.
- They are not for children, pregnancy, or people with fluid retention or amputations.
- The body fat method is only as good as the percentage you enter. Home scales and tape estimates can be several points off.
- Information only, not medical advice. Do not use it for drug dosing or other clinical decisions.
Common questions.
What is lean body mass?
Your weight minus your fat: muscle, bone, organs, skin and water. It is usually given in pounds or kilograms.
Which lean body mass formula should I use?
None is right for everyone. The calculator shows Boer, James and Hume together so you can see the spread. At high BMI use Boer or Hume, because the James formula turns down. If you know your body fat percentage, the body fat method is more direct.
How do I calculate lean body mass from body fat percentage?
Multiply your weight by (1 − body fat ÷ 100). At 82 kg and 20% body fat, lean body mass is 82 × 0.8 = 65.6 kg.
What is a normal lean body mass?
It depends on height, sex and build, so there is no single normal number. The formulas give typical values for a given height and weight. A DXA scan can compare you with reference data.
- Puri T, Blake GM. Comparison of ten predictive equations for estimating lean body mass with dual-energy X-ray absorptiometry in older patients. Br J Radiol 2022;95:20210378 — reproduces the Hume (1966) and Boer (1984) equations with original citations; DXA comparison in 1,558 adults aged 60–65; Hume pooled bias −1.1 kg
- Caruso D, De Santis D, Rivosecchi F, et al. Lean body weight-tailored iodinated contrast injection in obese patient: Boer versus James formula. Biomed Res Int 2018:8521893 — reproduces the Boer and James equations for men and women; James plateaus at a BMI of about 37 (women) and 43 (men)
- Hume R. Prediction of lean body mass from height and weight. J Clin Pathol 1966;19:389–391 — original Hume paper (abstract read): lean body mass from total body water by antipyrine space in 29 men and 27 women; r = 0.96 and 0.83
The Boer, James and Hume equations are evaluated in kilograms and centimeters as reproduced in the cited PMC papers, after exact conversion from pounds and inches. The James peak is found analytically, at the BMI where its slope is zero. Our tests check six cases worked separately in 40-digit decimal arithmetic, including Omni Calculator’s 75 kg, 180 cm example. They confirm on both sides that the James validity cut-off sits at the curve’s peak, and run 400 random bodies for U.S. and metric agreement, monotonicity in height and the lean and fat split. Further tests cover validation of every field and 500 extreme-input cases.
Built and reviewed by CalculatorLab against the sources above; every worked example on this page is re-checked by our automated test suite before each release. How we build and check calculators. Found a problem? Tell us.