Free body composition tool

Lean Body Mass Calculator

Calculate the weight of everything in your body except stored fat. Use a known body fat percentage for the most direct result, or compare Boer, James and Hume estimates from height, weight and sex.

4 methodsBody fat %, Boer, James and Hume.
Metric + imperialUse kg/cm or lb/in.
More than LBMSee fat mass, lean percentage and FFMI.
PrivateCalculations stay in your browser.
Note: Every result is an estimate. Hydration, body shape, age, training status and the source of your body fat value can change the result.

How to use the lean body mass calculator

A direct body-fat-based result is usually easier to interpret, while equations are useful when body fat is unknown.

Enter reliable measurements

Use current weight and height, preferably measured at the same time of day.

Add body fat if available

A DEXA, consistent BIA scale trend or careful circumference estimate can provide an input.

Choose the method

Auto uses body fat first; otherwise compare Boer, James, Hume or their average.

How to interpret lean body mass

Lean body mass includes muscle, bone, organs, water and other fat-free tissue; it is not the same as skeletal muscle mass.

  • Lean mass: Track the number over time instead of treating one estimate as a diagnosis.
  • Fat mass: The difference between body weight and estimated lean mass.
  • Lean percentage: Lean mass divided by total body weight.
  • FFMI: Lean mass adjusted for height; useful for consistent personal tracking.

Accuracy and limitations

Every result is an estimate. Hydration, body shape, age, training status and the source of your body fat value can change the result.

  • Not muscle mass: LBM includes water, bone and organs as well as muscle.
  • Equation bias: Population formulas may under- or over-estimate individuals.
  • Measurement noise: Hydration and device conditions can shift body fat readings.
  • Medical use: Do not use this page for medication dosing or clinical decisions.

Lean body mass formulas used

All equations use weight in kilograms and height in centimeters. The body-fat method is preferred when you have a reasonably measured body fat percentage.

MethodEquationBest used for
Body fat %LBM = weight × (1 − body fat ÷ 100)A known, reasonably measured body fat percentage.
BoerMen: 0.407W + 0.267H − 19.2; Women: 0.252W + 0.473H − 48.3General adult estimate from sex, height and weight.
JamesMen: 1.1W − 128(W/H)²; Women: 1.07W − 148(W/H)²Comparison with a nonlinear height-weight estimate.
HumeMen: 0.32810W + 0.33929H − 29.5336; Women: 0.29569W + 0.41813H − 43.2933A second linear estimate for comparison.

Worked examples

These examples show why the selected method matters.

Known body fat

70 kg at 18% body fat uses the direct method.

LBM: 57.4 kg; fat mass: 12.6 kg.

Formula estimate

A 175 cm, 70 kg male without a body fat input can compare three equations.

The average reduces dependence on one equation.

Progress tracking

Repeat the same method under similar hydration and timing conditions.

Trend direction matters more than tiny day-to-day changes.

Related body composition tools

Use these pages to estimate body fat, set a target or compare related measurements.

Body Fat Calculator

Estimate body fat from a photo.

Navy Body Fat Calculator

Estimate body fat from circumference measurements.

Body Recomposition Calculator

Turn current body composition into a target plan.

Healthy Body Fat Percentage

Compare body fat ranges by sex and age.

BMI Calculator

Compare weight relative to height.

Lean body mass calculator FAQ

Lean body mass is total body weight minus stored fat mass. It includes muscle, bone, organs, connective tissue and body water.

No. Muscle is one part of lean body mass, but LBM also includes water, bone, organs and other fat-free tissue.

Use Auto with a reasonably measured body fat percentage. If body fat is unknown, compare Boer, James and Hume rather than assuming one equation is exact.

Each equation was developed from different populations and mathematical assumptions, so individual estimates vary.

No. Clinical dosing may require a specific validated weight definition and professional judgment. Ask a qualified clinician.

For progress tracking, every two to four weeks under similar conditions is usually more useful than daily recalculation.

References and formula sources