Lean Body Mass Calculator
Estimate lean body mass with the Boer formula from sex, height and weight in metric or imperial units. Shows estimated lean and fat mass in kg and lb with a full formula breakdown.
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About the Lean Body Mass Calculator
Lean Body Mass Calculator estimates the part of your body weight that is not fat — muscle, bone, organs and water — using the Boer formula, one of the commonly used equations based on sex, height and weight. Enter your details in metric (kg, cm) or imperial (lb, feet and inches) units, and the tool shows estimated lean body mass and estimated fat mass in both kilograms and pounds.
A step-by-step formula breakdown shows exactly how each number was calculated. These are formula estimates, not measurements: they are not a body-composition scan such as DEXA and can differ noticeably from a measured result. The tool does not label or classify results and is not a target-setting tool; for personalised advice, consult a qualified healthcare professional.
How to use
- Choose metric or imperial units.
- Select the sex used by the formula and enter your age (adults only).
- Enter your height and weight.
- Click Calculate to see estimated lean body mass and fat mass in kg and lb.
- Review the formula breakdown, then copy or download the summary if you wish.
Key features
- Boer formula for males (0.407 × kg + 0.267 × cm − 19.2) and females (0.252 × kg + 0.473 × cm − 48.3).
- Metric and imperial input with exact conversions.
- Estimated lean body mass and fat mass in both kg and lb.
- Full formula breakdown with your numbers.
- Validation of age, height and weight ranges and implausible results.
- Copy Summary, Download Summary, Reset and Back.
Best practices
- Weigh yourself at a consistent time, for example in the morning.
- Use an accurate height measurement without shoes.
- Treat the result as a rough estimate, not a precise measurement.
- Compare results over time with the same method rather than across different tools.
- Talk to a healthcare professional before making changes based on body-composition numbers.
Benefits
- Understand roughly how body weight is split between lean and fat mass.
- Transparent calculation you can check yourself.
- Works in kilograms or pounds.
- Private: everything is calculated in your browser.
Frequently asked questions
What is the Boer formula?
It is a published equation that estimates lean body mass from height and weight, with separate coefficients for males and females: males 0.407 × weight (kg) + 0.267 × height (cm) − 19.2; females 0.252 × weight (kg) + 0.473 × height (cm) − 48.3.
How is estimated fat mass calculated?
Estimated fat mass is your total weight minus the estimated lean body mass. Because the lean mass is an estimate, the fat mass is an estimate too.
How accurate is it?
Formula estimates can differ noticeably from measured values, especially for very muscular people, older adults or people at the ends of the height and weight ranges. It is not a substitute for a body-composition scan.
Why does it ask for age?
Age is not part of the Boer formula. It is used to confirm the calculator is applied to an adult, because the formula was developed for adults.
Does it tell me whether my result is healthy?
No. The tool deliberately does not classify results or suggest targets. A qualified healthcare professional can interpret body composition in the context of your overall health.
Can I use pounds and feet?
Yes. Choose Imperial and enter weight in pounds and height in feet and inches. Results are shown in both kilograms and pounds.