Lean body mass equations and their limits
Compare three height-and-weight lean body mass equations, with an optional direct arithmetic estimate from entered body-fat percentage.
This page provides an equation-based estimate for education and planning. It does not diagnose a condition, measure an individual response, or replace professional care.
How to use this health calculator
- Choose appropriate inputs: Enter measurements using the units and ranges shown.
- Review the assumptions: Confirm that the model applies before interpreting the result.
- Calculate and interpret: Read the result together with its limitations and cautions.
- Use professional guidance when needed: Do not use a general calculator to change medication, treatment, or a clinician-directed plan.
Formula and variables
The formulas estimate rather than measure non-fat mass. Lean body mass and fat-free mass are often used similarly but are not perfectly identical physiological concepts.
Janmahasatian uses weight and BMI; Boer and Hume use sex-specific linear combinations of weight and height; fat-free mass = weight × (1 − body-fat fraction)- W — Weight
- Body weight converted to kilograms.
- H — Height
- Height converted to centimeters.
- BMI — Body mass index
- Weight kg divided by height meters squared.
Worked example: Janmahasatian equation
An adult enters 80 kg and 175 cm using the male equation.
- Weight
- 80 kg
- Height
- 175 cm
- BMI = 80 ÷ 1.75² = 26.12.
- Janmahasatian: 9270 × 80 ÷ (6680 + 216 × 26.12).
Result: The calculator returns the Janmahasatian estimate alongside Boer and Hume estimates.
Differences reflect equation design and uncertainty, not multiple true lean-mass values.
Understanding your results
Equation result
The numerical output follows the displayed formula and entered assumptions.
Personal interpretation
Individual biology, measurement error, environment, health conditions and medicines can change real-world outcomes.
Assumptions
- Height and weight are measured accurately.
- The binary equation input selects the intended published coefficients.
- Optional body-fat percentage comes from a known method and is entered as a percentage.
Limitations
- Anthropometric equations do not directly measure muscle, organs, bone or body water.
- Prediction error varies with body size, age, population and clinical condition.
- The formulas are not interchangeable with DXA, CT, MRI or other measured methods.
- An optional body-fat estimate carries the error of the method that produced it.
Common mistakes
- Calling lean body mass the same as skeletal muscle mass.
- Mixing pounds and kilograms.
- Treating small differences between equations as meaningful change.
- Using a general estimate for drug dosing without the required clinical protocol.
Practical use cases
Educational estimate
Explore how the inputs affect the equation result.
Consistent tracking
Compare estimates only when methods, units and conditions are consistent.
Planning and decision guide
Treat cautions as part of the result
Clinical dosing and imaging protocols may mandate a specific lean-weight equation and verification process.
Do not change medication, nutrition treatment or weight goals solely from this result.
Escalate symptoms or clinical questions
Seek qualified medical advice for symptoms, diagnosed conditions, medicines, pregnancy, or individualized treatment decisions.
Frequently asked questions
Is lean body mass the same as muscle mass?
No. It includes body water, organs, connective tissue and other non-fat components in addition to muscle.
Which equation should I use?
Use the equation required by the relevant validated protocol; otherwise compare them as estimates.
Is the body-fat option more accurate?
Only if the entered body-fat percentage is accurate; its measurement error transfers directly to the result.
Sources and review
- Quantification of Lean Bodyweight — Clinical Pharmacokinetics (PubMed record). Accessed 2026-08-03.
- Comparison of Ten Predictive Equations for Estimating Lean Body Mass with Dual-Energy X-Ray Absorptiometry in Older Patients — British Journal of Radiology via PubMed Central. Accessed 2026-08-03.
Reviewed 2026-08-03.