Financial term · Reviewed August 17, 2026
Lean body mass
Lean body mass: Total body weight minus estimated fat mass, covering muscle, bone, organs and water. The Lean Body Mass Calculator returns this figure from boer formula: men 0.407×kg + 0.267×cm − 19.2; women 0.252×kg + 0.473×cm − 48.3. At that calculator’s documented worked-example inputs the estimated lean body mass is 130; holding every other input steady, moving weight from 136 to 204 moves it from 116.2 to 143.9, a spread of 27.7.
Two people at the same weight can differ a lot in composition, and protein and calorie targets scaled to lean mass reflect that where targets scaled to total weight do not. For anyone training seriously the distinction is the difference between a useful target and an arbitrary one. Tracking it also separates two very different outcomes that a scale reports identically. Losing three kilograms of fat and losing three kilograms of muscle both read as three kilograms gone, and only one of them was the goal.
| Term | Lean body mass |
|---|---|
| Category | Body Composition |
| How it is found | Boer formula: men 0.407×kg + 0.267×cm − 19.2; women 0.252×kg + 0.473×cm − 48.3 |
| Worked example | Estimated lean body mass: 130 |
| Computed by | Lean Body Mass Calculator |
| Related terms | 6 defined in this glossary |
Before you rely on it
What to check
Note which method produced the figure.
The common error
Where people go wrong with lean body mass
Treating a formula estimate from height and weight as a measurement. Those are much less accurate than a direct assessment.
Worked through
Lean body mass in plain numbers
A person weighs 80 kg and has an estimated body fat of 20%. Fat mass is 16 kg, so lean body mass is 80 − 16 = 64 kg. Suppose they lose 4 kg of weight over three months. If 3 kg of that is fat and 1 kg is lean tissue, lean mass is now 63 kg out of 76 kg total, and body fat has fallen to about 17.1%. The scale alone would show a 4 kg drop, while the lean and fat split tells you what kind of loss it was. Estimates of body fat come from calipers, scales that measure impedance, scans or formulas, each with its own error.
Easily confused
Lean body mass and its neighbours
Lean body mass is not muscle mass. It includes muscle, bone, organs, connective tissue and water, everything except fat. Fat-free mass is a near synonym. Skeletal muscle mass is a smaller subset. It is also different from BMI, which uses only height and weight, and from body fat percentage, which is its complement; a person can have the same weight and BMI as another but a very different lean mass. Estimation methods differ in whether they include essential fat, so figures from different sources may not match.
In real decisions
Where lean body mass turns up
Athletes and trainers track it to see whether training is building tissue. It helps set protein and calorie targets. Clinicians use it to scale some drug doses and to assess nutrition and frailty. Someone dieting checks it to make sure weight lost is mostly fat. Calculators estimate it from height, weight, sex and sometimes measurements; comparing trends over time is more useful than any single reading, because methods have consistent biases.
Know the edges
Where lean body mass stops being reliable
Formulas give population-based estimates that can be well off for individuals. Hydration, food intake and time of day affect impedance readings. Very muscular, very lean or older people may be misestimated. Body composition measurement is imprecise, and small changes may be noise. This page is educational and not medical advice. For health decisions, consult a qualified professional who can use appropriate methods.
Quick answers
What people ask about lean body mass
How can I estimate my lean mass at home? Formulas use height, weight and sex, and some scales estimate it by impedance. Both are approximations. Compare trends under consistent conditions.
Put it to work
How lean body mass is calculated
At the lean body mass calculator’s worked-example inputs, estimated lean body mass is 130, estimated fat mass is 40. Moving weight from 136 to 204 moves that first figure from 116.2 to 143.9.
Open the Lean Body Mass Calculator →
These are population-based formulas, not diagnoses. Frame size, muscle mass, ethnicity and other factors these formulas do not measure can shift what is healthy for a given person. Consult a healthcare provider for individual guidance.
Related vocabulary
Terms used alongside this one
Keep reading
Nearby in the glossary
- ← Internal rate of return (IRR)
- Least common multiple (LCM) →
- All 174 defined termsThe complete Free Calculators Online financial glossary.