Lean Body Mass Calculator
Calculate your lean body mass (LBM) — your weight minus body fat. Used for setting protein targets, calorie needs, and tracking body composition progress.
Did this tool work for you?
How to use this calculator
If body fat % is unknown, the Boer formula estimates LBM from height and weight: LBM = 0.407W + 0.267H − 19.2 (men); 0.252W + 0.473H − 48.3 (women).
- 1
Enter your body weight, height, and sex.
- 2
If you know your body fat percentage (from DEXA, calipers, or smart scales), enter it for a precise result.
- 3
Leave body fat at 0 to use the Boer estimation formula from height and weight.
Frequently asked questions
Which method is used when I enter a body fat percentage?
The calculator multiplies your weight by (1 − body fat ÷ 100). A 75 kg person entering 20% gets 75 × 0.8 = 60 kg of lean mass and 15 kg of fat mass. The accuracy of the answer is exactly the accuracy of the body fat figure you supplied.
What does it do when I leave body fat at 0?
It switches to the Boer formula. For men that is 0.407 × weight (kg) + 0.267 × height (cm) − 19.2, and for women 0.252 × weight + 0.473 × height − 48.3. The body fat percentage shown is then derived from that estimate, and the Method row tells you which route was used.
Why was my body fat entry ignored?
Only values above 0 and below 100 are used. Zero (which is also what a cleared box becomes), a negative value, or 100 or more falls back to the Boer estimate without a warning, so check the Method line in the results to confirm what was applied.
Can I enter pounds? What about height in feet?
Weight can be entered in kilograms or pounds; pounds are divided by 2.20462 internally, and lean mass is shown in both kg and lb. Height must be in centimetres, and there is no feet-and-inches field.
Where does the protein figure come from?
It is simply lean mass in kilograms multiplied by 2.2, rounded to whole grams. That multiplier is a fixed value in the code, not a personal recommendation, and it is not adjusted for age, kidney health or training. Ask a dietitian or doctor what suits you.
Can the Boer estimate produce odd results?
Yes. It uses only height, weight and sex, so it can look unrealistic at extremes. For a woman of 100 kg and 150 cm it returns 47.9 kg lean and a 52.1% fat share. The formula cannot see muscle, so treat it as a rough starting point rather than a measurement.
What does lean body mass include?
Everything that is not fat mass: muscle, bone, organs, skin and body water. A drop in lean mass after dieting can therefore be water or muscle, and the calculator cannot tell which. It is general information and not medical advice.
Lean body mass — two ways the calculator works it out
Subtracting fat from total weight
Lean body mass is body weight minus fat mass. When you give the calculator a body fat percentage it keeps the arithmetic simple: weight times one minus the fat fraction. It also reports fat mass in kilograms, the body fat percentage, lean mass in both kilograms and pounds, and a protein figure derived from the lean value. All of this rests on the percentage you supply, which may come from a scan, calipers or a smart scale.
The Boer estimate without a measurement
When body fat is left at zero the tool predicts lean mass from height and weight alone, with different coefficients for each sex.
| Sex | Weight (kg) | Height (cm) | Constant |
|---|---|---|---|
| Male | × 0.407 | × 0.267 | − 19.2 |
| Female | × 0.252 | × 0.473 | − 48.3 |
Worked examples
Each result comes from running the calculator. A 75 kg, 175 cm man with no body fat entered gets a Boer estimate of 58.0 kg lean (128.0 lb), 17.0 kg fat and an implied 22.6% fat. Entering 20% for the same man gives 60.0 kg lean, 15.0 kg fat and a 132 g protein figure. A woman weighing 150 lb at 165 cm with no percentage entered is converted to about 68.0 kg and gets 46.9 kg lean and 31.1% fat. A 60 kg, 165 cm woman who enters 28% gets 43.2 kg lean and 16.8 kg of fat.
Why two routes can disagree
The percentage route reflects whatever your measuring method says; the formula route reflects an average person of your height and weight. In the male example the two routes differ by 2.0 kg of lean mass. A trained person usually carries more lean mass than the Boer equation predicts, and the equation cannot register it, so a measured percentage is the better input when you have one.
Tracking changes over time
Lean mass is most useful as a trend taken with the same method each time, since different devices give different percentages for the same person. Compare like with like and expect small day-to-day swings from hydration and food intake. The protein line is a fixed multiple of lean mass and not individualised advice. This page is general information, not medical advice.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →