Lean Body Mass Calculator — 3 Scientific Formulas

Calculate your lean body mass (LBM) using Boer, Hume, and James formulas. Get estimated fat mass and body fat percentage instantly. Free, science-based calculator.

Medically reviewed by Dr. Ivan IbáñezNº Col. 17/05487Mar 31, 2026

How to use this calculator?

CalcVita. (2026). Lean Body Mass Calculator — 3 Scientific Formulas. CalcVita. Retrieved September 2, 2026, from https://calcvita.com/en/calculators/lean-body-mass

Lean Body Mass: What It Is, Why It Matters, and How to Measure It

Lean body mass is the weight of everything in your body that is not fat — muscles, bones, organs, and water. Learn how to calculate it using Boer, Hume, and James formulas, and why it matters more than total body weight for health and performance.

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How does this calculator work?

This calculator uses three validated formulas — Boer (1984), Hume (1966), and James (1976) — to estimate lean body mass from weight, height, and sex. Lean body mass (LBM) is the portion of your body weight that is not fat. It includes muscles, bones, organs, and body water. The average of all three formulas is displayed as the primary result.

About the formulas

The Boer formula was derived from densitometry studies and is widely used in clinical settings. Hume developed his equation using data from hospitalized patients, making it useful across a broad weight range. The James formula, while simple, can underestimate LBM in individuals with higher BMI. All three are used in drug dosing, sports science, and body composition research.

Limitations

These formulas were derived from population samples and may not accurately reflect individual body composition. They do not account for ethnicity, fitness level, or disease state. For precise measurements, clinical methods such as DEXA scanning or underwater weighing should be used. Consult a healthcare professional for medical decisions.

Sources

Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol 1984;247(4 Pt 2):F632-6. PMID: 6496691
Hume R. Prediction of lean body mass from height and weight. J Clin Pathol 1966;19(4):389-391. PMID: 5929341
James WPT. Research on Obesity. Her Majesty's Stationery Office, London, 1976.

Frequently asked questions

What is lean body mass?: Lean body mass (LBM) is the total weight of your body minus all fat mass. It includes muscles, bones, organs, skin, and body water. LBM is a key metric in sports science, clinical nutrition, and drug dosing calculations.
Which LBM formula is most accurate?: No single formula is universally best. The Boer (1984) formula is considered the most accurate for most adults. The Hume (1966) formula performs well across weight ranges, while the James (1976) formula can underestimate LBM in obese individuals. Comparing all three provides the most complete picture.
How is lean body mass different from muscle mass?: Lean body mass includes all non-fat tissue: muscles, bones, organs, fluids, and glycogen. Muscle mass is just one component of LBM. To measure muscle mass precisely, methods like DEXA scanning or bioelectrical impedance analysis are needed.
Why does lean body mass matter?: LBM determines your basal metabolic rate, influences drug dosing in clinical settings, predicts athletic performance, and is used to set protein and calorie targets. Higher LBM is associated with better metabolic health, stronger bones, and lower risk of chronic disease.

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Frequently asked questions

What is lean body mass?

Lean body mass (LBM) is the total weight of your body minus all fat mass. It includes muscles, bones, organs, skin, and body water. LBM is a key metric in sports science, clinical nutrition, and drug dosing calculations.

Which LBM formula is most accurate?

No single formula is universally best. The Boer (1984) formula is considered the most accurate for most adults. The Hume (1966) formula performs well across weight ranges, while the James (1976) formula can underestimate LBM in obese individuals. Comparing all three provides the most complete picture.

How is lean body mass different from muscle mass?

Lean body mass includes all non-fat tissue: muscles, bones, organs, fluids, and glycogen. Muscle mass is just one component of LBM. To measure muscle mass precisely, methods like DEXA scanning or bioelectrical impedance analysis are needed.

Why does lean body mass matter?

LBM determines your basal metabolic rate, influences drug dosing in clinical settings, predicts athletic performance, and is used to set protein and calorie targets. Higher LBM is associated with better metabolic health, stronger bones, and lower risk of chronic disease.