FFMI Calculator
Know your muscle mass index
Enter your height, weight, and body fat percentage to calculate your FFMI.
An objective measure of muscle development — free, no signup.
FFMI = lean mass (kg) ÷ height (m)² · normalized
| Rank | Male | Female |
|---|
* Based on Kouri et al. (1995), derived from a Western population sample. Values may skew slightly higher than averages observed in East Asian populations.
Track your FFMI with AI insights
AIFitLog logs your workouts and body composition automatically.
AI reviews your weekly progress and tells you what to focus on next.
Available in English and Japanese
FFMI (Fat-Free Mass Index) measures the amount of muscle mass you carry relative to your height, independent of body fat. Unlike BMI, it isn't skewed by fat mass, making it a more useful metric for people who train seriously.
This calculator uses the normalized FFMI formula: lean body mass (kg) divided by height (m)², then adjusted for height using the correction +6.1 × (1.8 − height in meters). This normalization levels the playing field between taller and shorter individuals.
How to use: Enter your height, weight, and body fat percentage. For best accuracy, use a DEXA scan or calibrated body composition scale for your body fat reading — the quality of your FFMI result depends directly on the accuracy of that input.