Lean Body Mass CalculatorFree online fitness & health calculator — instant results, no sign-up
Lean mass using Boer, James and Hume formulas.
For general information only. This is not medical advice, diagnosis, dosing guidance or a treatment recommendation. Talk to a doctor or other qualified health professional about your health, pregnancy, or diet.
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About the Lean Body Mass Calculator
This calculator estimates your Lean Body Mass (LBM)—the weight of your body minus all body fat—using three standard anthropometric formulas: Boer, James, and Hume. It provides side-by-side estimates based strictly on sex, total body weight, and height.
- Sex
- Biological sex (Male or Female), which determines the specific regression coefficients used in each equation.
- Height
- Total standing body height, measured in centimeters (cm). Typical values range from 120 cm to 230 cm.
- Weight
- Total body weight, measured in kilograms (kg). Typical values range from 30 kg to 250 kg.
Formula and method
Boer Formula: Male: LBM = 0.407 × W + 0.267 × H − 19.2 Female: LBM = 0.252 × W + 0.473 × H − 48.3 James Formula: Male: LBM = 1.1 × W − 128 × (W / H)^2 Female: LBM = 1.07 × W − 148 × (W / H)^2 Hume Formula: Male: LBM = 0.3281 × W + 0.33929 × H − 29.5336 Female: LBM = 0.29569 × W + 0.41813 × H − 43.2933
- LBMLean body mass in kilograms (kg)
- WTotal body weight in kilograms (kg)
- HHeight in centimeters (cm)
The calculator evaluates the three equations independently using the entered weight, height, and sex selection. Each resulting value is rounded to one decimal place and displayed in kilograms.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- SexMale
- Height175 cm
- Weight75 kg
Results
- Boer58 kg
- James59 kg
- Hume54.4 kg
How to use the Lean Body Mass Calculator
- 1Select your biological sex to determine the appropriate mathematical constants for each equation.
- 2Enter your standing height in centimeters and current total body weight in kilograms.
- 3Calculate the three values: Boer and Hume use linear combinations of weight and height minus a constant, while James subtracts a squared ratio of weight to height scaled by a factor.
- 4Round each resulting lean mass figure to one decimal place.
Reading your result
The outputs represent estimated fat-free tissue (muscle, bone, organs, and water) under three clinically published statistical models. While they generally yield values within a few kilograms of each other for average physiques, variations arise because each formula was developed on different sample populations.
Limitations
These formulas rely entirely on height and weight and do not directly measure tissue density or body fat percentage. Consequently, they can underestimate lean mass in heavily muscled athletes or overestimate lean mass in individuals with high body fat levels. The James formula is also known to produce declining lean mass estimates at very high body weights due to its quadratic penalty.
Common questions
What is the difference between lean body mass and fat-free mass?+
The terms are often used interchangeably in everyday fitness. Technically, lean body mass includes a small amount of essential fat contained in the central nervous system and internal organs (roughly 2–3% in men and 5–8% in women), whereas fat-free mass excludes all lipids.
Why do the three formulas give different values?+
Each formula was derived from regression analysis on different demographic sample sets using distinct clinical measurement methods (such as total body water or radiotracers), leading to slightly different mathematical relationships between height, weight, and fat-free tissue.
Why does the James formula drop sharply at very high weights?+
The James equation includes a subtracted term proportional to the square of weight divided by height ((W / H)^2). At very high body mass index values, this subtracted term grows faster than the linear weight term, causing estimated lean mass to paradoxically decrease.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.