Offline Website BuilderCalculate your Fat-Free Mass Index, lean body mass, and height-adjusted FFMI.
Enter your body weight, height, and body fat percentage to calculate your FFMI.
FFMI is an estimate, not a medical diagnosis. Accuracy depends heavily on the reliability of your body fat measurement. Lean body mass includes more than muscle: it also includes water, bones, organs, and other non-fat tissues.
The Fat-Free Mass Index (FFMI) compares your lean body mass with your height. It is similar in structure to Body Mass Index (BMI), but uses fat-free body mass rather than total body weight. This makes FFMI a useful additional measure when evaluating body composition in fitness and strength training.
First, your estimated fat-free body mass is calculated using your body weight and body fat percentage. That value is then divided by your height in meters squared.
Lean Body Mass = Body Weight × (1 − Body Fat % / 100)
FFMI = Lean Body Mass (kg) / Height (m)²
Normalized FFMI applies a height adjustment to the standard FFMI value. A commonly used equation references a height of 1.80 meters, or approximately 5 feet 11 inches.
Normalized FFMI = FFMI + 6.1 × (1.80 − Height in Meters)
A higher FFMI can indicate more fat-free mass relative to height. However, FFMI is not a direct measurement of skeletal muscle mass. Differences in hydration, bone mass, and other tissues can affect the result.
| BMI | FFMI |
|---|---|
| Uses total body weight | Uses estimated fat-free body mass |
| Requires weight and height | Also requires body fat percentage |
| Does not distinguish fat from lean tissue | Provides additional body composition context |
FFMI can help track estimated changes in fat-free mass over time. However, a single result should not be interpreted in isolation. Age, sex, measurement methods, and individual physical characteristics all influence how the value should be understood.
FFMI alone cannot reliably determine whether someone uses performance-enhancing substances. It should not be treated as proof of natural or enhanced bodybuilding.
Enter your body weight in pounds and your height in feet and inches, or switch to kilograms and centimeters. Measurements are automatically converted when you change systems. FFMI and normalized FFMI remain unit-independent, while fat mass and lean body mass are displayed in the selected weight unit.
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