Lean Body Mass Calculator
Estimate your lean body mass (LBM) from your sex, age, height and body weight using the Boer formula, with metric and imperial unit support.
Calculate Your Lean Body Mass
Enter your details below to estimate lean body mass. Age is included for the profile summary, while the Boer equation itself uses height, weight and sex.
Your Results
| Sex | — |
| Age | — |
| Height | — |
| Weight | — |
| Estimated fat mass | — |
Step-by-Step Calculation
What Is Lean Body Mass?
Lean body mass (LBM) is an estimate of the portion of body weight that is not stored body fat. It includes muscle, bones, organs, body water and other lean tissues.
Lean body mass is not the same as muscle mass. Muscle is only one component of lean body mass, so an LBM result should not be interpreted as your total muscle weight.
How Is Lean Body Mass Calculated?
This FreeCalz calculator uses the Boer formula. The equation uses body weight in kilograms, height in centimetres and a sex-specific set of coefficients.
Female: LBM = (0.252 × weight in kg) + (0.473 × height in cm) − 48.3
If you enter pounds or inches, the calculator converts them to kilograms and centimetres before applying the formula.
Lean Body Mass Example
Suppose a male weighs 75 kg and is 175 cm tall.
LBM = 30.525 + 46.725 − 19.2
LBM = 58.05 kg
The estimated lean body mass is approximately 58.1 kg.
Lean Body Mass vs. Fat Mass
Body weight can be viewed broadly as lean mass plus fat mass. Because the Boer calculation estimates lean mass, an approximate fat-mass value can be derived by subtracting estimated LBM from total body weight.
This derived fat-mass figure should also be treated as an estimate because the LBM itself is predicted rather than directly measured.
Lean Body Mass Percentage
For an additional way to view the result, the calculator estimates the percentage of body weight represented by the predicted lean mass:
This percentage is a mathematical result from the same equation; it is not a clinically measured body-composition percentage.
Does Age Affect Lean Body Mass?
Age is collected by this calculator for your result summary and to keep the tool within an adult-use range. The Boer equation used here does not contain age as a variable; it uses sex, body weight and height.
How Accurate Is a Lean Body Mass Calculator?
A formula-based LBM calculator provides an estimate rather than a direct body-composition measurement. Accuracy depends on the equation and how closely an individual resembles the population represented by the equation.
More direct body-composition techniques can include DEXA, air-displacement methods and hydrostatic weighing. These methods also have assumptions and measurement error, so results should be interpreted in context.
Who Can Use This Calculator?
- Adults who want a general estimate of lean body mass.
- People tracking body weight and body-composition trends over time.
- Fitness users who want a simple LBM estimate for educational purposes.
- Anyone who wants to compare their calculated LBM with other body-composition information.
This version is intended for adults aged 18 and above. It should not be used as a pediatric body-composition calculator.
Tips for Tracking Lean Body Mass
- Measure body weight under similar conditions when comparing results.
- Use consistent height and weight units.
- Focus on trends rather than a single calculated value.
- Do not assume that a change in LBM is entirely a change in muscle.
- For clinical or highly accurate body-composition assessment, use an appropriate professional measurement method.
Lean Body Mass Calculator FAQs
What does LBM stand for?
LBM stands for lean body mass. It refers to an estimate of body weight excluding stored body fat.
Is lean body mass the same as muscle mass?
No. Lean body mass includes muscle as well as bone, organs, body water and other lean tissues.
What formula does this calculator use?
This calculator uses the Boer formula, with separate equations for males and females.
Does the Boer formula use age?
No. The Boer equation uses sex, body weight and height. Age is collected for the calculator profile and result summary.
Can I calculate LBM in pounds and inches?
Yes. Select Imperial mode. The calculator converts pounds to kilograms and inches to centimetres internally.
What is the difference between LBM and fat-free mass?
The terms are often used similarly in consumer fitness contexts. Scientific definitions can differ slightly depending on how essential fat is classified.
Can athletes use this calculator?
Yes, as a rough estimate, but highly muscular physiques may not be represented well by a height-and-weight prediction equation.
Can children use this calculator?
No. This calculator is designed for adults aged 18 and above and should not be used as a child growth or body-composition tool.
Why can my calculated LBM differ from a body scanner?
A scanner or other body-composition method measures or estimates composition using a different methodology. A simple equation cannot be expected to match every measurement method.
Can LBM be used to plan a diet?
LBM can provide context for fitness calculations, but this calculator should not be used by itself to prescribe an individualized diet or medical treatment.
How often should I calculate LBM?
For general tracking, periodic measurements under similar conditions are more useful than repeatedly checking small short-term changes.
Is this calculator medical advice?
No. It is an educational estimation tool. Consult a qualified healthcare professional for clinical body-composition assessment or medical decisions.
Methodology
The calculator validates adult age, height and weight inputs, converts imperial measurements to kilograms and centimetres when needed, calculates BMI, applies the sex-specific Boer equation, and reports estimated lean mass, lean-mass percentage and derived fat mass. The displayed step-by-step section shows the arithmetic used for the entered values.
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Disclaimer
Important: This calculator provides an estimated lean body mass for general informational purposes only. It does not directly measure body fat, muscle mass, bone mass, body water or other tissues. Actual body composition varies between individuals, and formula-based estimates may differ from professional measurements. Do not use this result alone to diagnose a health condition or make medical decisions.