Boer equation
Men: 0.407W + 0.267H − 19.2Women: 0.252W + 0.473H − 48.3W is kilograms and H is centimeters. Boer developed estimated lean body mass as an index for normalizing body-fluid volumes in healthy adults.
Body composition calculator
Lean Body Mass Calculator
Estimate lean body mass using four recognized height-and-weight equations, compare how the formulas differ, and optionally calculate lean mass directly from a body-fat percentage you already know.
4 published equations Browser-side calculation kg & lb outputs
Free LBM calculator
Estimate and compare your lean body mass
Enter adult height and body weight, select the sex-specific equation set, and choose which formula should appear as your primary result. Body-fat percentage is optional.
Formula comparison
Recognized lean body mass equations used by this calculator
All four equations use adult height, weight and sex-specific coefficients, but they were developed for different purposes and populations. That is why the results should be compared rather than treated as interchangeable measurements.
Janmahasatian equation
Men: (9270W) ÷ (6680 + 216×BMI)Women: (9270W) ÷ (8780 + 244×BMI)Developed to estimate fat-free/lean body weight across a population that included extremes of body size. It avoids the mathematical downturn seen with James at high BMI.
James equation
Men: 1.10W − 128(W/H)²Women: 1.07W − 148(W/H)²W is kilograms and H is centimeters. This older equation remains widely cited, but its squared term can make it unreliable at high body mass.
Hume equation
Men: 0.32810W + 0.33929H − 29.5336Women: 0.29569W + 0.41813H − 43.2933Hume derived sex-specific prediction equations from total-body-water estimates in a small adult clinical sample.
Important: these are regression estimates, not direct body-composition measurements. Two people with the same height, weight and sex receive the same formula estimate even if their muscularity and fat distribution differ.
Understand the result
What lean body mass includes—and what it does not tell you
Lean body mass is commonly treated as body weight excluding most fat mass. In practical fitness calculations it is often used similarly to fat-free mass, although the terms are not perfectly identical in physiology.
More than muscle
LBM includes skeletal muscle, organs, bone, connective tissue and body water—not just the muscle you train in the gym.
Useful for trends
Repeated estimates can add context to weight-change goals, but day-to-day hydration and measurement error can obscure small changes.
No universal “ideal”
There is no single healthy LBM number that applies to everyone. Height, sex, age, frame size, sport and goals all matter.
Fitness application
How to use LBM without over-interpreting it
Lean mass estimates are most useful when paired with consistent measurement habits and a goal that actually benefits from body-composition context.
Track weight-loss quality
When losing weight, monitor training performance, circumference changes and body-composition trends to help distinguish fat loss from unwanted loss of lean tissue.
Set protein context
Some sports-nutrition approaches use body weight or lean mass to frame protein targets. Use evidence-based intake ranges and avoid treating an estimated LBM as exact.
Compare methods consistently
If you track LBM over time, use the same equation and the same measurement conditions. Switching formulas can create a change that did not occur in your body.
Use better measurements when needed
For clinical decisions, athletic assessment or precise body-composition work, use an appropriate validated measurement method and qualified professional interpretation.
Input quality
Get more repeatable height and weight inputs
Formula precision does not compensate for inconsistent measurements. Use repeatable conditions when comparing results over time.
Measure height without shoes
Stand upright on a level surface with your head in a neutral position. Use the same height for repeated calculations unless it is re-measured accurately.
Use a stable body-weight measurement
For trend tracking, weigh under similar conditions—often at a similar time of day, on the same scale, with similar clothing.
Do not mix units
The calculator converts imperial inputs before applying equations. If calculating manually, formulas shown here use kilograms and centimeters.
Treat body fat as optional evidence
Only enter body-fat percentage if you have a meaningful estimate. Guessing body fat can make the direct calculation less informative than the formula comparison.
Tool guide
Understand and use the Lean Body Mass Calculator
Use these tool-specific notes to understand the method, enter better data, interpret the output, and apply the result appropriately.
What LBM Includes
Lean body mass is total body mass minus fat mass. It includes muscle, bone, organs, body water, and other fat-free tissues—not muscle alone.
Choose an Equation
The calculator can compare published LBM prediction equations such as Boer, James, Hume, and Janmahasatian. Different equations may produce different values because they were derived from different populations.
Enter Size Data
Weight, height, and sex/category inputs are used according to the selected regression. Unit conversions happen before calculation so metric and imperial entries remain comparable.
Interpret Carefully
Predicted LBM is not the same as a measured body-composition scan. Large changes in hydration, body size, or population characteristics can reduce equation accuracy.
Frequently asked questions
Lean Body Mass Calculator FAQs
Practical answers about this tool's inputs, method, results, limitations, and common real-world use.
What is lean body mass?
Lean body mass is the portion of body weight that is not stored fat. It includes muscle, organs, bone, connective tissue and body water. In many calculator contexts it is used similarly to fat-free mass, though the terms are not physiologically identical.
Which LBM formula should I use?
There is no universally best equation for every body type and purpose. Boer is a common general estimate; Janmahasatian was developed to behave more consistently across extremes of body size; James and Hume remain useful historical comparisons.
Why does the James formula sometimes look unusual?
James subtracts a squared weight-to-height term. At high body mass relative to height, the equation can turn downward and produce implausible values. This calculator flags formula outputs that exceed basic physiological bounds.
Can I calculate fat mass from LBM?
Yes arithmetically: estimated fat mass = total body weight − estimated LBM. Remember that if LBM is estimated by a regression equation, the resulting fat mass is also only an estimate.
Is LBM the same as muscle mass?
No. Muscle is only one component of lean body mass. LBM also includes organs, bone, body water and other non-fat tissues.
Does more LBM always mean better fitness?
No. LBM depends strongly on total body size and includes non-muscle tissue. Fitness should be evaluated with measures relevant to your goal, such as strength, endurance, health markers, body composition and performance.
Is lean body mass the same as muscle mass?
No. Skeletal muscle is only one part of lean body mass. LBM also includes water, organs, bone, connective tissue, and other non-fat components.
Can I calculate body-fat percentage from predicted LBM?
You can derive an implied fat mass from body weight minus estimated LBM, but that compounds the prediction error. Treat it as an estimate rather than a measured body-fat percentage.
Which lean-body-mass equation is best?
There is no universal winner for every population. Comparing several published equations can show how much model choice affects the estimate.
Why can hydration affect lean-mass interpretation?
A large portion of fat-free mass is water. Short-term fluid changes can alter measured body weight and body-composition methods, so a single estimate should not be overinterpreted.
Method & references
Formula sources and limitations
The calculator applies the published equations in kilograms and centimeters after converting imperial inputs. Results are estimates and should not be used as a substitute for a measured body-composition assessment when accuracy matters.
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol. 1984.
- Janmahasatian S, et al. Quantification of lean bodyweight. Clin Pharmacokinet. 2005.
- Han PY, et al. Review of body-size descriptors in obesity, including limitations of the James equation.
- Hume R. Prediction of lean body mass from height and weight. J Clin Pathol. 1966.
- Clinical comparison paper listing Hume, Boer and James equations against CT-derived lean body mass.
Content reviewed: .
Health-use disclaimer
This calculator is for adult educational and fitness use. Prediction equations do not directly measure body composition and can be less reliable at unusual body sizes, during pregnancy, with significant fluid shifts, or in highly atypical muscularity. Do not use this page to determine medication dosing or make clinical decisions without a qualified healthcare professional.