FFMI Calculator
Estimate fat-free mass relative to height and compare a height-normalized FFMI.
Your FFMI Result
Result status:
Practical interpretation
Important: Estimate only—not medical advice.
How the FFMI Calculator works
Formula: Lean mass = weight × (1 − body fat ÷ 100); FFMI = lean mass ÷ height²; normalized FFMI = FFMI + 6.1 × (1.8 − height in meters).
Weight is converted to kilograms and height to meters. The normalized equation adjusts the index toward a reference height of 1.8 m.
Assumptions and limits: Body-fat measurement error directly affects FFMI, and practical ranges are descriptive rather than diagnostic or proof of drug use. Results are estimates for education and planning, not medical advice.
How to use your result
Use the result as a starting point, not a pass-or-fail score. Keep your inputs consistent, observe relevant trends over time, and adjust only when the trend—not one day—shows the estimate does not fit your needs.
Body measurements and equation-based targets always contain uncertainty. If your result conflicts with symptoms, a diagnosis, medication guidance, pregnancy needs, an eating-disorder recovery plan, or instructions from your care team, follow your qualified health professional.
Frequently Asked Questions
What does the FFMI Calculator calculate?
It estimates estimate fat-free mass index, normalized ffmi, and lean mass.. The result is an educational planning estimate rather than a clinical assessment or guaranteed performance outcome.
What formula does the FFMI Calculator use?
Lean mass = weight × (1 − body fat ÷ 100); FFMI = lean mass ÷ height²; normalized FFMI = FFMI + 6.1 × (1.8 − height in meters). The full method and assumptions are displayed above the references.
Can I enter metric or imperial measurements?
Yes. Imperial mass and height entries are converted to kilograms and centimeters before calculation, while results use your selected display system.
How accurate is the FFMI Calculator?
It is best used as a starting point. Body-fat measurement error directly affects FFMI, and practical ranges are descriptive rather than diagnostic or proof of drug use.
How should I use the result in training or nutrition planning?
Apply it conservatively, keep inputs and measurement conditions consistent, and use multi-week trends in performance or body weight before adjusting your plan.
When should I recalculate?
Recalculate after a meaningful change in body weight, training performance, activity, or another required input—not in response to normal day-to-day fluctuations.
Who should seek individualized guidance?
Minors, pregnant people, competitive athletes with specialized demands, and anyone with an injury, medical condition, or eating-disorder history should consult an appropriately qualified professional.
Is this result medical advice?
No. The calculator cannot account for a diagnosis, medication, injury, laboratory result, or instructions from your health care team.
Scientific References
- Fat-free mass index in users and nonusers of anabolic-androgenic steroids Clinical Journal of Sport Medicine
- Body Composition and Health National Institutes of Health Office of Dietary Supplements
- ACSM Guidelines for Exercise Testing and Prescription American College of Sports Medicine