Lean Body Mass Calculator
Estimate your lean body mass from height and weight, or from your body fat percentage.
Calculation Examples
How to Use the Lean Body Mass Calculator
Enter your weight and height. If you have a recent body fat percentage (from skinfold calipers, bioelectrical impedance, or a DEXA scan), enter it too, because it gives the most direct result. Choose metric or imperial units and click "Calculate."
The tool shows your lean body mass, which is everything in your body except fat. Tracking it helps you confirm that a change on the scale is fat and not muscle or bone. This is an estimate for education and fitness tracking, not medical advice or a dosing tool.
How Lean Body Mass Calculations Work
When body fat percentage is known, lean body mass is direct: \(LBM = W \times (1 - BF/100)\), where \(W\) is weight and \(BF\) is body fat in percent. An 80 kg person with 20% body fat has \(LBM = 80 \times 0.80 = 64\ \text{kg}\) and 16 kg of fat. Without body fat, the calculator uses height and weight formulas, with \(W\) in kg and \(H\) in cm. The Boer formula (1984), common in clinical pharmacokinetics, is \(LBM = 0.407W + 0.267H - 19.2\) for men and \(LBM = 0.252W + 0.473H - 48.3\) for women. The James formula (1976) is \(LBM = 1.1W - 128(W/H)^2\) for men and \(1.07W - 148(W/H)^2\) for women. The Hume formula (1966) is \(0.3281W + 0.33929H - 29.5336\) for men and \(0.29569W + 0.41813H - 43.2933\) for women. All three are population averages, so they miss for people with unusually high or low muscle mass.
Useful Tips 💡
- Measure under the same conditions every time: same time of day (morning, after using the bathroom), same scale, and similar hydration. Body water counts as lean mass, so hydration can move your result by 1 to 2 kg.
- DEXA (dual-energy X-ray absorptiometry) gives the best body fat percentage to feed the calculator. Skinfold calipers and bioelectrical impedance scales are practical alternatives with more variability.
📋Steps to Calculate
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Enter your body weight and height in your preferred units.
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Enter your body fat percentage if known, for the most accurate direct calculation.
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Click "Calculate" to receive lean body mass estimates from multiple formulas alongside the body fat mass.
Mistakes to Avoid ⚠️
- Treating lean body mass as muscle mass. LBM includes organs, bone, blood, water, and connective tissue as well as muscle. Skeletal muscle is roughly 40% to 50% of LBM in healthy adults.
- Comparing results while hydration changes. Dehydration lowers the reading and rehydration raises it, even though muscle and organs have not changed.
- Trusting the formulas for very muscular athletes. Boer, James, and Hume were built on general populations, so they tend to underestimate LBM for people with unusually high muscle mass.
Practical Applications📊
Check a cut: an 80 kg person at 20% body fat (64 kg lean) who drops to 76 kg at 15.8% still has 64 kg lean, so the 4 kg lost was fat. If the same 76 kg showed 18% body fat, lean mass would be 62.3 kg, and about 1.7 kg of the loss was lean tissue.
Estimate resting energy: the Katch-McArdle equation, BMR = 370 + 21.6 x LBM (kg), gives about 1,752 kcal a day for 64 kg of lean mass. Cunningham's equation, 500 + 22 x LBM, gives about 1,908 kcal.
Compare formulas: for a 180 cm, 90 kg man, Boer gives 65.5 kg, James gives 67.0 kg, and Hume gives 61.1 kg, a spread of nearly 6 kg from the same inputs.
Understand drug dosing research: clinical studies sometimes dose by lean mass, because fat tissue takes little part in how some drugs are distributed. Doses must always come from a prescriber, not from this tool.