Lean Body Mass Calculator
Estimate lean body mass using the Boer, James and Hume formulas.
About Lean Body Mass Calculator
Lean Body Mass (LBM) is total body weight minus fat mass. It includes muscle, bone, water, and organs. Unlike total weight, LBM is directly tied to metabolic rate, drug dosing, and protein requirements. Three established formulas are shown because each was validated in a different clinical context — comparing them reveals the degree of uncertainty in any single prediction.
Formulas
Boer (1984) — male
LBM = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2
- W
- Weight in kg
- H
- Height in cm
Boer (1984) — female
LBM = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3
- W
- Weight in kg
- H
- Height in cm
James (1976) — male
LBM = 1.1 × weight − 128 × (weight/height)²
- W
- Weight in kg
- H
- Height in cm
Hume (1966) — male
LBM = 0.3281 × weight + 0.33929 × height − 29.5336
- W
- Weight in kg
- H
- Height in cm
Worked example
With the default values below, Lean Body Mass Calculator returns Average LBM (all formulas) of 57.2. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Biological Sexone of Male, Female
- Male
- Unitsone of Metric (kg, cm), Imperial (lb, in)
- Metric (kg, cm)
- Weight (kg)accepts 20–300 kg
- 75 kg
- Height (cm)accepts 100–250 cm
- 175 cm
- Weight (lb)accepts 44–660 lb
- 165 lb
- Height (in)accepts 39–98 in
- 69 in
Results
- Average LBM (all formulas)
- 57.2 kg
- Boer (1984)
- 58.1 kg
- James (1976)
- 59.0 kg
- Hume (1966)
- 54.4 kg
- Estimated Fat Mass (Boer basis)
- 17.0 kg
- Estimated Body Fat %Derived from Boer LBM; use the Body Fat Calculator for a tape-measure estimate.
- 22.6 %
Step by step
- 1Input (metric)= 75 kg, 175 cm, male
- 2Boer LBM= 58.1 kg
- 3James LBM= 59 kg
- 4Hume LBM= 54.4 kg
Assumptions and limits
- The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
- LBM estimates from height and weight carry ±3–5 kg error compared to DEXA scanning. This tool is for informational purposes only and is not a substitute for clinical body composition assessment.
- This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
LBM estimates from height and weight carry ±3–5 kg error compared to DEXA scanning. This tool is for informational purposes only and is not a substitute for clinical body composition assessment.
Frequently Asked Questions
Why do the three formulas give different results?
Each formula was derived from a different population and era. Boer (1984) is based on bioelectrical impedance in European subjects; James (1976) on UK data; Hume (1966) on a small Canadian cohort. No single equation is universally superior, so the average across all three is the most robust single figure to use.
What is LBM used for in medicine?
LBM is used to calculate drug doses (especially chemotherapy and antibiotics), GFR (kidney function), and target weights for ICU nutritional support. Total body weight would overdose larger individuals; LBM-adjusted dosing is more accurate and safer.
How does LBM differ from fat-free mass?
Fat-free mass (FFM) and LBM are often used interchangeably, but strictly speaking LBM includes essential fat in the nervous system, bone marrow and organs (~3% for men, ~8–12% for women). FFM is zero fat. In practice the difference is small enough that most clinical references treat them as equivalent.