Estimated Lean Body Mass
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{{ format(fatKg) }} kg fat {{ fatPercent.toFixed(1) }} % fat
Formula LBM (kg) LBM (lb) Body Fat (%)
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Introduction:

Lean body mass (LBM) is the portion of your weight that is not fat: muscle, bone, organs, water and other fat-free tissues. Because LBM drives basal energy needs and athletic potential, knowing it contextualises weight changes better than body mass index or scale readings alone. Clinicians also reference LBM when calculating drug dosages and monitoring recovery.

Enter your weight, height and sex, then select a recognised clinical formula. A reactive engine instantly applies the equation, converts units automatically and presents lean body mass, fat mass and body-fat percentage. A charting layer and comparison table let you inspect four formulas side-by-side, spotlighting how methodology affects numerical results.

Use the estimate to fine-tune calorie targets, adjust resistance-training volume or decide whether a gaining or cutting phase makes sense today. Athletes may track weekly trends, while clinicians may cross-check bedside measures during recovery. This calculator offers informational estimates, not medical advice; consult a qualified professional before making health or dosing decisions.

Technical Details:

Concept Overview

Lean body mass calculations rely on anthropometric regression models that link observable measurements (weight and stature) to laboratory-measured fat-free mass obtained via hydrostatic weighing or dual-energy X-ray absorptiometry. The Boer, James, Hume and Janmahasatian equations adjust for sex, height and nonlinear weight relationships to approximate composition without imaging equipment. Estimating LBM supports drug dosing, sports nutrition and longitudinal monitoring across diverse age groups and clinical settings where direct measurement tools are unavailable.

Core Equations

Boer

LBM=0.407W+0.267H19.2

(replace with 0.252 · W + 0.473 · H − 48.3 for female)

James

LBM=1.10W128W2/H2

(use 1.07 and 148 for female)

Hume

LBM=0.32810W+0.33929H29.5336

(replace with 0.29569 · W + 0.41813 · H − 43.2933 for female)

Janmahasatian

LBM= 9270W 6680+216 WH2

Interpretation

Body-Fat CategoryMen (%)Women (%)
Essential fat2–510–13
Athletes6–1314–20
Fitness14–1721–24
Acceptable18–2425–31
Obese>25>32

Compare your calculated fat percentage to the ranges above to contextualise health status and performance potential; aim for gradual, sustainable changes.

Variables & Parameters

ParameterMeaningUnitTypical Range
WBody weightkg30–200
HStanding heightcm120–220
SexCoefficient selectormale / female
FormulaRegression modelBoer · James · Hume · Janmahasatian

Worked Example

Boer (male) with 70 kg and 175 cm:

0.40770=28.49 0.267175=46.73 28.49+46.7319.2=56.02

LBM ≈ 56.0 kg; body-fat ≈ 20 %.

Assumptions & Limitations

  • Derived from adult cohorts; accuracy drops for children.
  • Pregnancy and oedema add non-fat mass that distorts estimates.
  • Self-reported measurements undermine reliability.
  • Formulas approximate, not replace imaging-based assessments.

Edge Cases & Error Sources

  • Mixing imperial inputs with metric units.
  • Negative or zero values entered accidentally.
  • Very high muscle mass outside regression scope.
  • Rapid water shifts after rehydration events.

Scientific Validity & References

Formulas originate from peer-reviewed studies: Boer 1984, James 1976, Hume 1966, and Janmahasatian 2005. Comparative analyses report mean absolute errors under 3 kg against DXA benchmarks.

Privacy & Compliance

No personal data leaves your device, supporting GDPR-aligned data minimisation.

Step-by-Step Guide:

Follow these steps to obtain a quick composition snapshot.

  1. Type your weight, then select kilograms or pounds.
  2. Enter your height and choose centimetres or inches.
  3. Select sex for sex-specific coefficients.
  4. Pick the formula; Boer opens by default.
  5. Review results and explore the comparison or breakdown tabs.
  6. Ensure both measurements are positive numbers before trusting outputs.

FAQ:

Is my data stored?

Everything runs locally; no values are transmitted or saved.

Which formula is most accurate?

Accuracy varies by population. Boer offers balanced performance, but comparing all four captures uncertainty.

Why does my scale disagree?

Smart scales use bio-impedance, which fluctuates with hydration. Regression equations rely only on weight and height.

Is this suitable for children?

The models target adults; paediatric-specific equations are required for reliable child assessment.

How often should I recalculate?

Weekly measurements under similar conditions reveal meaningful trends without day-to-day noise.

Glossary:

Lean Body Mass
Weight of everything except fat tissue.
Fat-Free Mass
Alternate term for lean body mass.
Body-Fat Percentage
Percent of weight that is adipose tissue.
Regression Equation
Statistical formula linking inputs to outcome.
Anthropometry
Measurement of human body dimensions.