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BMI Calculator
Body Mass Index with WHO classification and healthy weight range.
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Lean Body Mass Calculator
Lean mass in kg or lbs from weight and body fat %, or via Boer / James / Hume formulas. No signup — your inputs stay in your browser.
Step By Step
How to Use This Calculator
4 steps
- Enter your total body weight in kg or lbs using the unit toggle.
- Choose 'Height-based formula' if you do not know your body fat %, or 'Known body fat %' for a more direct calculation.
- For the formula method, also enter your height in cm and select your sex — the Boer, James and Hume formulas each require these values.
- The result shows LBM as a weight and as a percentage, plus fat mass for reference.
Worked Example
Example: Male, 80 kg, 178 cm
Use this sample to sanity-check your inputs and understand what the final result represents.
- 1Boer: 0.407 × 80 + 0.267 × 178 − 19.2 = 32.56 + 47.53 − 19.2 = 60.89 kg LBM
- 2James: 1.1 × 80 − 128 × (80/178)² = 88 − 128 × 0.2018 = 88 − 25.83 = 62.17 kg LBM
- 3Hume: 0.3281 × 80 + 0.3393 × 178 − 29.53 = 26.25 + 60.40 − 29.53 = 57.12 kg LBM
- 4Average: (60.89 + 62.17 + 57.12) / 3 ≈ 60.1 kg LBM
Final Result
Estimated LBM ≈ 60.1 kg (75.1% of body weight). Fat mass ≈ 19.9 kg (24.9%).
Methodology
Boer (1984), James (1976), Hume (1966)
This section explains the calculation logic, assumptions, and source material used to make the result more trustworthy and easier to verify.
Boer — Male: LBM = 0.407W + 0.267H − 19.2. Female: LBM = 0.252W + 0.473H − 48.3. James — Male: LBM = 1.1W − 128(W/H)². Female: LBM = 1.07W − 148(W/H)². Hume — Male: LBM = 0.3281W + 0.3393H − 29.5336. Female: LBM = 0.2969W + 0.4150H − 43.2933. Body fat method: LBM = W × (1 − BF%/100). W in kg, H in cm.
Frequently Asked Questions
What is lean body mass (LBM)?+
Lean body mass is total body weight minus fat mass. It includes muscle, bone, organs, connective tissue, and total body water. It is sometimes used interchangeably with fat-free mass (FFM), though strictly speaking FFM excludes essential lipids while LBM includes a small amount of essential fat within organs and the central nervous system. In practice, for most non-clinical purposes, the two terms are treated as equivalent.
What formulas does this calculator use?+
The calculator uses three validated anthropometric formulas. The Boer formula (1984, published in Clinical Physiology) was derived from underwater weighing studies. The James formula (1976) is widely cited in pharmacokinetics for drug dosing. The Hume formula (1966, Journal of Clinical Pathology) was developed from cadaveric studies. Because each uses different regression coefficients derived from different populations, their results can differ by 1–3 kg. The average of all three is presented as the best single estimate.
How is LBM used in practice?+
LBM is used in several clinical and fitness contexts. In pharmacology, many drug doses — particularly for antibiotics and chemotherapy agents — are calculated based on LBM or ideal body weight rather than total weight to avoid over-dosing in obese patients. In fitness, LBM is used to calculate protein requirements (a common target is 1.6–2.2 g of protein per kg of LBM daily, per the ISSN position stand), track muscle gain while accounting for fat changes, and estimate basal metabolic rate more accurately than total weight alone.
How is the body fat percentage method different from the formulas?+
The body fat % method is a direct arithmetic calculation: LBM = Total weight × (1 − Body fat % ÷ 100). It is more accurate than the anthropometric formulas if you have a reliably measured body fat percentage — from DEXA scan, hydrostatic weighing, or the validated Navy tape method. The height-and-weight formulas estimate LBM without needing body fat data, making them useful when body fat has not been measured, but they carry more estimation error.
What body fat percentage should I aim for?+
Healthy body fat ranges vary by sex and age. For men, the American Council on Exercise (ACE) defines 6–13% as athletic, 14–17% as fit, 18–24% as acceptable, and above 25% as obese. For women: 14–20% athletic, 21–24% fit, 25–31% acceptable, above 32% obese. Essential fat (required for organ function and hormonal health) is approximately 2–5% for men and 10–13% for women — going below these levels is harmful.