Lean Body Mass Calculator
Estimate your lean body mass and fat mass — from your body-fat percentage if you know it, or the Boer formula from your height and weight.
Lean body mass is your weight minus its fat portion: with a measured body-fat percentage, LBM = weight × (1 − body-fat%/100); otherwise the Boer (1984) formula estimates it from sex, height and weight.
What lean body mass tells you
Lean body mass is everything in your body that isn't fat — muscle, bone, organs, water and connective tissue. Tracking it alongside fat mass is a better gauge of body composition than the scale alone: two people at the same weight can have very different amounts of muscle and fat. If your weight stays flat while lean mass climbs and fat mass drops, you're recomposing.
The most accurate way to get LBM is to feed in a measured body-fat percentage: lean mass is just your weight minus the fat portion. If you don't have one, this tool uses the Boer formula, which estimates lean mass from your sex, height and weight. You can get a body-fat figure first with the body fat calculator.
Making sense of the number
Height-and-weight formulas are population averages, so treat the result as an estimate — they're least accurate for very muscular, very lean, or very high-body-fat people. What matters most is the trend over time under consistent conditions. To see how your lean mass compares for your height, pair this with the FFMI calculator, and check overall status with BMI.
Estimated lean body mass by profile (Boer)
| Profile | Lean mass (Boer) | Fat mass |
|---|---|---|
| Male, 70 kg, 175 cm | 56.0 kg | 14.0 kg |
| Male, 80 kg, 180 cm | 61.4 kg | 18.6 kg |
| Male, 90 kg, 185 cm | 66.8 kg | 23.2 kg |
| Male, 100 kg, 190 cm | 72.2 kg | 27.8 kg |
| Female, 55 kg, 160 cm | 41.2 kg | 13.8 kg |
| Female, 60 kg, 165 cm | 44.9 kg | 15.1 kg |
| Female, 70 kg, 170 cm | 49.8 kg | 20.2 kg |
| Female, 80 kg, 175 cm | 54.6 kg | 25.4 kg |
Boer (1984) estimates; fat mass = weight − lean mass. A measured body-fat percentage, when available, is more accurate than any formula.
Formula: Boer (1984). Estimates are population averages, least accurate at the extremes of body size — not a body-composition measurement or medical advice.
Frequently asked questions
What is lean body mass (LBM)?
Lean body mass is your total body weight minus the mass of your fat. It includes muscle, bone, organs, connective tissue and body water. Strictly, LBM includes the small amount of essential fat inside cells, while 'fat-free mass' excludes all fat — the two differ by only a few percent and are often used interchangeably in fitness contexts.
Which method should I use — body fat % or the Boer formula?
If you have a real body-fat percentage from a DEXA scan, BodPod, or skinfold assessment, use it: LBM = weight × (1 − body-fat%/100). It is the most accurate path. If you do not, this calculator falls back to the Boer (1984) equation, which estimates LBM from your sex, weight and height and is the standard used in clinical references.
Why do lean-mass formulas give different answers for the same person?
Each equation (Boer, James, Hume) was fitted to a different study population and era, so their coefficients differ. They agree best for average-sized adults and diverge most at the extremes of height and weight — which is exactly where an actual measured body-fat percentage becomes worth getting.
Does lean body mass tell me how much muscle I have?
Not directly. LBM lumps muscle together with bone, organs, connective tissue and water, so it is always considerably larger than your skeletal muscle mass. It is still useful for tracking trends: if your weight holds steady while estimated LBM rises and fat mass falls, that is consistent with recomposition. For an actual muscle figure you need imaging like DEXA or MRI.
How accurate are height-and-weight LBM estimates?
They are population averages, not personal measurements. Because they use only sex, weight and height, they cannot account for your individual muscularity, frame size or hydration, and error grows for athletes and very lean or very high-body-fat individuals. Use them for rough tracking and pair them with a periodic measured body-composition test when accuracy matters.
Sources
- Boer P. (1984), Am J Physiol — via PubMed — Boer formula used for LBM
- Hume R. (1966), J Clin Pathol — via PubMed — Alternative lean body mass equation
- National Academies Press (1990), Body Composition — NCBI Bookshelf — Lean vs fat mass assessment
The thresholds and formulas used by this calculator follow the primary sources above. This tool provides general information, not personalised medical advice.