Lean Body Mass Calculator
Estimate lean body mass with Boer, James and Hume formulas using height, weight and sex, with metric and imperial support.
Enter your values
Change any assumption and calculate again to compare results.
What lean body mass means
Lean body mass is body weight minus estimated fat mass. It includes muscle, bone, organs, water and other non-fat tissue, so it should not be interpreted as “muscle mass.”
This calculator compares three published anthropometric equations—Boer, James and Hume. Because they were derived from different populations and assumptions, the estimates can differ. Showing all three makes that uncertainty visible instead of presenting one formula as exact.
Why formulas disagree
Height-and-weight equations cannot directly measure body composition. Hydration, muscularity, age and body-fat distribution can cause two people with the same height and weight to have different lean mass.
For a more direct body-composition assessment, clinical or laboratory methods may be used. For everyday planning, formula estimates can still be useful for rough comparisons over time when the same method is used consistently.
Using the result
The calculator reports each formula in kilograms and pounds and also provides a simple average. Do not use the average as a medical reference value; it is only a convenient summary of the formula outputs.
If an equation returns an implausible result for an extreme height or weight, interpret it cautiously. These formulas work best within ordinary adult body-size ranges.
Important information
This calculator is for general education and planning. It is not a diagnosis, medical device or substitute for individualized healthcare advice. Measurements and formula estimates can differ from clinical assessments.
If the result could affect treatment, pregnancy care, medication, driving, military status or another safety-sensitive decision, confirm it with the appropriate qualified professional or official process.
Frequently Asked Questions
Is lean body mass the same as muscle mass?
No. Lean body mass includes muscle plus bone, organs, body water and other non-fat tissue.
Which formula is best?
There is no universally best equation for every person. This calculator shows Boer, James and Hume side by side.
Can I enter pounds and inches?
Yes. Choose imperial units and the calculator converts internally before applying the formulas.