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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Categories: Calculator , Health & Fitness
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Lean Body Mass (LBM) is everything in your body that is not fat: muscle, organs, bone, water, and connective tissue. Tracking LBM alongside total weight provides a clearer picture of physique changes than relying on scales or Body Mass Index alone.

This calculator converts weight and height to metric units, applies four peer-reviewed medical equations, and returns lean mass, fat mass, and body-fat percentage. A reactive engine updates tables, comparison bars, and a composition pie the moment you alter any input.

For example, a 70 kg male at 175 cm yields 57.4 kg lean mass with the Boer equation. Results offer informational estimates only - they are not medical advice.

Technical Details:

Foundational Principles

Direct measurement of body composition requires imaging or densitometry, yet empirical formulae can approximate lean mass within clinically acceptable error when weight, height, and sex are known. Each formula embeds population-specific regression coefficients derived from hydrodensitometry or isotope dilution studies performed on healthy adults. By running all four models concurrently, the tool offers a sensitivity analysis that highlights how methodological assumptions shift results.

Formula Overview

Variables & Parameters

SymbolMeaningUnitTypical RangeSensitivity
WBody weightkg40 - 200High
HStaturecm130 - 210Moderate
BMIBody Mass Indexkg m-215 - 45Derived
SSex (0 F / 1 M)-binaryCategorical

Scoring & Categorisation

  • Body-fat < 10 % — Athletic
  • 10 % - 20 % — Healthy
  • 20 % - 25 % — Overfat
  • > 25 % — Obese risk zone

Representative Calculations

Edge Cases & Assumptions

  • Weights below 30 kg round to the nearest 0.05 kg.
  • Extremely short adults (< 120 cm) may yield negative James outputs.
  • Zero or null inputs invalidate all calculations.
  • Formulae were calibrated on adults; paediatric use is unreliable.

Performance & Stability

The numeric workload is O(1); each refresh involves four scalar equations and a small charting layer update. All computation occurs client-side, eliminating network latency and ensuring privacy. Double-precision floats provide ±0.01 kg accuracy under typical ranges.

Step-by-Step Guide:

  1. Enter your weight and choose kilograms or pounds.
  2. Enter your height; select centimetres or inches.
  3. Select sex; this toggles male/female coefficients.
  4. Pick a preferred formula or keep the default Boer recommendation.
  5. View the summary box; switch tabs to compare formulae, inspect the pie break-down, or download a CSV.

FAQ:

Why four formulas?

Using multiple equations surfaces methodological variance and helps you judge confidence by convergence or spread.

Which formula is most accurate?

Accuracy depends on age, ethnicity, and body type. Boer fits average adults well; James penalises high BMI strongly.

Is my data stored?

No. All inputs stay in your browser and vanish when you close or refresh the page.

Can I use this for children?

These equations were validated on adults; paediatric estimation requires specialised models and measurement tools.

What if my lean mass looks low?

Verify units first. If correct, discuss results with a qualified professional before changing diet or training.

Glossary:

Lean Body Mass
Total mass excluding fat.
Body-Fat %
Fat mass divided by total weight.
Boer Equation
Regression model tuned for adults.
BMI
Weight-to-height ratio kg/m².
Sensitivity
How strongly a variable moves the output.

No data is transmitted or stored server-side.

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