Lean Body Mass Calculator
Estimate your lean body mass using multiple validated formulas.
Results
What is Lean Body Mass?
Lean body mass (LBM) is everything in your body that is not fat: muscles, bones, organs, skin, blood, and body water. Subtract your fat mass from your total weight and the remainder is lean body mass. Two people of identical weight can carry very different amounts of lean tissue, so LBM is often more informative than the scale alone.
LBM has practical uses: athletes track it to confirm training is adding muscle rather than fat, clinicians use it when sizing certain drug doses, and protein recommendations scale with lean tissue better than with total weight. Since measuring body composition directly requires specialized equipment such as a DEXA scan, researchers built equations that estimate LBM from just weight, height, and gender — this calculator runs the three most widely used ones side by side.
The Boer, James, and Hume Formulas
Each formula takes weight in kilograms and height in centimeters and returns an estimated lean body mass in kilograms. For men, the equations are:
Boer: LBM = (0.407 × weight) + (0.267 × height) − 19.2
James: LBM = (1.1 × weight) − 128 × (weight ÷ height)²
Hume: LBM = (0.32810 × weight) + (0.33929 × height) − 29.5336
For women, the coefficients differ:
Boer: LBM = (0.252 × weight) + (0.473 × height) − 48.3
James: LBM = (1.07 × weight) − 148 × (weight ÷ height)²
Hume: LBM = (0.29569 × weight) + (0.41813 × height) − 43.2933
- Weight — your total body weight. If you enter pounds, the calculator converts to kilograms first (1 lb = 0.45359237 kg).
- Height — your standing height. Inches are converted to centimeters (1 in = 2.54 cm).
- Gender — selects the coefficient set, because typical body composition differs between men and women.
The calculator then averages the three estimates and divides by your weight to give your LBM percentage — the share of your weight that is lean tissue.
Worked Example: A Man Weighing 80 kg at 180 cm
Suppose a man enters 80 kg and 180 cm. Each formula gives its own estimate:
- Boer: (0.407 × 80) + (0.267 × 180) − 19.2 = 32.56 + 48.06 − 19.2 = 61.42 kg
- James: (1.1 × 80) − 128 × (80 ÷ 180)² = 88 − 128 × 0.19753 ≈ 88 − 25.284 = 62.716, which rounds to 62.72 kg
- Hume: (0.32810 × 80) + (0.33929 × 180) − 29.5336 = 26.248 + 61.0722 − 29.5336 = 57.79 kg
The average is (61.42 + 62.716 + 57.7866) ÷ 3 = 181.9226 ÷ 3 ≈ 60.6 kg of lean body mass. Dividing by total weight gives 60.64 ÷ 80 = 0.758, an LBM percentage of 75.8%. The complement — roughly 80 − 60.64 ≈ 19.4 kg — is fat mass. In imperial units the same man enters about 176.4 lb and 70.9 in, which convert back to roughly 80.0 kg and 180.1 cm, giving effectively identical results.
Average LBM for Common Body Sizes
Average of the three formulas for common heights and weights, with LBM percentage in parentheses.
| Height | Weight | Avg LBM (Male) | Avg LBM (Female) |
|---|---|---|---|
| 160 cm | 55 kg | 44.7 kg (81.3%) | 40.8 kg (74.2%) |
| 170 cm | 65 kg | 51.6 kg (79.4%) | 47.8 kg (73.5%) |
| 170 cm | 75 kg | 55.7 kg (74.2%) | 50.8 kg (67.7%) |
| 175 cm | 70 kg | 55.1 kg (78.7%) | 51.3 kg (73.3%) |
| 180 cm | 80 kg | 60.6 kg (75.8%) | 56.3 kg (70.4%) |
| 190 cm | 90 kg | 67.6 kg (75.1%) | 63.4 kg (70.4%) |
How to Use
- Choose Metric (kg, cm) or Imperial (lb, in); the weight and height labels update to match.
- Select Male or Female from the Gender dropdown.
- Enter your weight and height in the units shown.
- Click Calculate to see the Boer, James, and Hume estimates, the average LBM, and your LBM percentage.
- Click Reset to clear the form.
Frequently Asked Questions
Which formula is most accurate?
All three are validated estimation methods fitted to different study populations; none is universally most accurate for every individual. In the worked example above, the estimates span 57.79 kg to 62.72 kg — a spread of about 5 kg — which is typical. Averaging the three, as this calculator does, gives a reasonable middle estimate; precise measurement requires a DEXA scan or similar body-composition test.
What is a healthy LBM percentage?
It varies by gender and fitness level. Men typically range from 75-90% and women from 65-85%, with trained athletes at the higher end. Because LBM percentage and body fat percentage are exact complements, a higher LBM percentage means a leaner body composition.
Does LBM include water weight?
Yes. Lean body mass includes all non-fat tissue — muscle, bone, organs, skin, blood, and body water — and water alone makes up a large share of it. Because hydration shifts daily, true LBM can move slightly even when muscle mass has not changed.
What is the difference between lean body mass and muscle mass?
Muscle mass refers only to skeletal muscle, while lean body mass includes muscle plus bones, organs, skin, blood, and water. LBM is therefore always larger than muscle mass — in the 80 kg worked example above, much of the 60.6 kg of lean mass is not muscle. Gaining muscle raises LBM, but so do increases in water, bone, or organ tissue.
Why do the three formulas give different results?
Each equation was fitted to a different dataset and measurement method, so the coefficients differ. The James formula also curves downward at higher weights because of its squared (weight ÷ height) term, while Boer and Hume are linear. Small disagreements of a few kilograms are normal, which is why the calculator shows all three and highlights the average.
Can I use this for medication dosing?
This calculator provides estimates only. Some medications are dosed using lean body mass, but clinical dosing follows drug-specific guidelines and professional judgment. Always consult a healthcare provider or pharmacist for any dosing decision.