Free body composition & weight tool
Lean Body Mass Calculator: Boer, James and Hume Formulas
Lean body mass is your total weight minus fat mass. When you only know height, weight and sex, three published formulas estimate it: Boer, James and Hume. For an 80 kg, 180 cm man they give 61.4, 62.7 and 57.8 kg of lean mass. The calculator below runs all three side by side so you can see how much they agree.
Prepared by Prospyr · Reviewed October 3, 2026 · Free, no sign-up, runs in your browser
Predictions from height and weight only, not a body scan. Decision support only; it does not replace clinical judgment.
Lean body mass (range across the three formulas)
126.9 to 138.5lb
Boer (1984)
135.6 lb
Fat mass 44.4 lb (24.7% of weight)
James (1976)
138.5 lb
Fat mass 41.5 lb (23.1% of weight)
Hume (1966)
126.9 lb
Fat mass 53.1 lb (29.5% of weight)
Lean mass vs fat mass, by formula
- Boer75.3% lean
- James76.9% lean
- Hume70.5% lean
lean mass everything else (fat mass)
Lean body mass formulas: Boer, James and Hume
Weight (W) is in kilograms and height (H) is in centimeters. The calculator converts from pounds and inches for you.
| Formula | Men | Women |
|---|---|---|
| Boer (1984) | 0.407 W + 0.267 H − 19.2 | 0.252 W + 0.473 H − 48.3 |
| James (1976) | 1.10 W − 128 (W ÷ H)² | 1.07 W − 148 (W ÷ H)² |
| Hume (1966) | 0.32810 W + 0.33929 H − 29.5336 | 0.29569 W + 0.41813 H − 43.2933 |
Worked example
A man who is 180 cm and 80 kg. Boer: 0.407 × 80 + 0.267 × 180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.4 kg. James: 1.10 × 80 − 128 × (80 ÷ 180)² = 88 − 25.3 = 62.7 kg. Hume: 0.32810 × 80 + 0.33929 × 180 − 29.5336 = 26.25 + 61.07 − 29.53 = 57.8 kg.
A woman who is 165 cm and 65 kg gets 46.1 kg (Boer), 46.6 kg (James) and 44.9 kg (Hume). Fat mass in each case is weight minus the lean mass estimate, so the three formulas imply body fat between 28.3% and 30.9% for her.
Lean body mass vs body fat percentage
Lean body mass and fat mass add up to body weight, so each formula also implies a body fat percentage. That implied figure is a prediction from height and weight only. For a number built from tape measurements, use the body fat percentage calculator, and for BMI the BMI calculator.
Practices that track body composition over time can keep each visit's measurements in the patient chart next to the visit note.
Limits of these estimates
All three formulas predict from height and weight, so two people with the same numbers but different muscle get the same answer. A 2022 comparison with DXA scans in adults aged 60 to 65 found 95% limits of agreement of roughly 11 to 13 kg even for the best of ten equations. Use the range across formulas as a sense of the uncertainty. This tool does not make a clinical judgment.
Frequently asked questions
How do you calculate lean body mass?
Without a body scan, you estimate it from height, weight and sex with a prediction formula such as Boer, James or Hume. The calculator runs all three. If you already know your body fat percentage, lean mass is simply weight × (1 − body fat ÷ 100).
What is the Boer formula for lean body mass?
For men, LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2. For women, LBM = 0.252 × weight + 0.473 × height − 48.3. Boer published it in 1984 while normalizing blood and extracellular fluid volumes.
What is the difference between the Boer, James and Hume formulas?
They were fitted to different groups with different methods, so they give different numbers for the same person. James (1976) uses weight and the square of weight over height, Hume (1966) was fitted to lean mass measured by total body water, and Boer (1984) is a straight linear fit. For an 80 kg, 180 cm man they differ by about 5 kg.
Which lean body mass formula is the most accurate?
No single formula wins everywhere. A 2022 study compared ten equations with DXA scans in 1,558 adults aged 60 to 65 and found other equations (Gallagher and Janmahasatian) performed best, with 95% limits of agreement still around 11 to 13 kg. Treat any of these as a rough estimate.
What is the difference between lean body mass and fat-free mass?
The two terms are often used interchangeably, and their exact definitions vary by author and by measurement method. The formulas on this page predict lean body mass as each author defined it, so treat the numbers as estimates for comparison, not exact accounting.
Why does the James formula give a low result at high weights?
The James equation subtracts a term based on weight squared, so past a certain weight the predicted lean mass falls even as weight rises. For a 175 cm man, that turns around near 132 kg. The calculator flags this and shows the other two formulas for comparison.
Sources and scope
- Regional anesthesia in obese patients: Challenges, considerations, and solutions. Saudi J Anaesth, 2025 (PMC12007849)
Peer-reviewed table printing the Boer, James and Hume lean body mass equations for men and women (weight in kg, height in cm).
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol, 1984 (PubMed 6496691)
Original Boer paper; lean mass estimated from body weight and height.
- Hume R. Prediction of lean body mass from height and weight. J Clin Pathol, 1966 (PubMed 5929341)
Original Hume paper; lean mass from total body water (antipyrine space) in 56 adults.
- Comparison of ten predictive equations for estimating lean body mass with dual-energy X-ray absorptiometry in older patients. Br J Radiol, 2022 (PMC10993957)
747 men and 811 women aged 60 to 65; Gallagher and Janmahasatian equations performed best; limits of agreement 10.7 to 12.8 kg.
Estimates from published prediction formulas, not a body scan. Decision support only; it does not replace clinical judgment. It does not set a dose, diet or treatment.