How to use the lean body mass calculator
Enter your height, weight and sex, and the calculator estimates your lean body mass three ways at once — the Boer, James and Hume formulas — plus a live bar showing the lean-vs-fat split of your body weight. If you already know your body fat percentage from a DEXA scan, BodPod, or skinfold caliper, enter it under Go advanced for an exact figure instead of an estimate.
The exact formula (if you know your body fat %)
If you don't know your body fat percentage, the body fat calculator estimates it from tape-measure measurements.
The three classic estimate formulas
| Formula | Year | Tends to… |
|---|---|---|
| Boer | 1984 | The most common modern clinical reference |
| James | 1976 | Read slightly higher for average male body sizes |
| Hume | 1966 | Read slightly lower vs. modern DEXA validation |
None of the three is "the" correct answer — they were built from different research cohorts decades apart and routinely disagree by 2–5 kg at the same body size. That spread is the honest measure of uncertainty in any estimate that only uses height and weight.
What counts as a healthy lean body mass?
As a rough guide, a lean body mass of about 75–86% of total weight for men and 69–79% for women is typical, based on common body-fat-percentage guidelines. Athletes often sit above this range; it naturally shifts with age, training, and build — it isn't a strict pass/fail line.
Why lean body mass matters
- Tracking a diet or training program. The scale can't tell you whether weight lost was fat or muscle — lean body mass can.
- Setting a protein target. Most modern protein guidelines (roughly 1.6–2.2 g per kg of lean mass for active adults) reference lean mass, not total body weight.
- Drug dosing. Some medications, particularly water-soluble drugs, are dosed by lean body weight rather than total weight.
Once you have a lean-mass figure, the protein intake calculator turns it into a daily gram target.
Lean body mass for children
The Boer, James and Hume formulas were all derived from adult cohorts and don't apply to growing children. For ages 14 and younger, this calculator switches to the Peters formula, which estimates lean mass from an estimated extracellular fluid volume instead.
Common questions
How do I calculate my lean body mass?
If you know your body fat percentage, lean body mass = weight × (1 − body fat %). If you don't, formulas like Boer, James and Hume estimate it from your height, weight and sex alone. This calculator does both automatically.
What is a healthy lean body mass percentage?
Roughly 75–86% of total body weight for men and 69–79% for women is considered a typical healthy range, based on common body-fat-percentage guidelines. Athletes often sit above this range; it varies by age and build.
Which lean body mass formula is most accurate?
No single formula is correct for everyone. Boer (1984) is the most commonly used modern clinical reference. James (1976) tends to read slightly higher for average male body sizes, and Hume (1966) tends to read lower. The three routinely disagree by 2–5 kg at the same body size, which is the honest measure of uncertainty in any height-and-weight-only estimate.
Why does lean body mass matter?
Lean body mass drives most of your metabolism, is what many drug-dosing protocols use instead of total body weight, and is a better way to track a weight-loss or training program than the number on the scale alone, since it separates muscle from fat.
How is lean body mass different from fat-free mass?
They're used almost interchangeably. Strictly, fat-free mass excludes the small amount of essential fat inside cell membranes and the nervous system, which lean body mass formulas include. The difference is usually only 2–3% of body weight and rarely matters outside research settings.