Track resistance-training progress
Compare FFMI over time while using a consistent body-fat measurement method rather than relying on scale weight alone.
FFMI Calculator
Enter your weight, height, and estimated body-fat percentage to calculate FFMI, lean mass, and a research-based height-normalized value instantly.
Everyday Calculators
Calculate Your FFMI
Enter weight, height, and an estimated body-fat percentage. Results update as you type.
Your FFMI result will appear here
Complete all three measurements to calculate automatically.
FFMI depends strongly on body-fat measurement accuracy. The optional height normalization follows the male-athlete model reported by Kouri et al. and is not a diagnosis or proof of drug use. Review the original study.
What Is FFMI Calculator?
An FFMI calculator estimates fat-free mass index: the amount of lean mass relative to height. Unlike BMI, which uses total weight, FFMI first removes the estimated mass attributed to body fat. It is commonly used to track physique and resistance-training progress.
This page also reports a height-normalized FFMI using the equation published by Kouri and colleagues in a 1995 study of male athletes. That adjustment is useful as research context, but its sample does not make it a universal diagnostic cutoff for every sex, age, ethnicity, or body type.
How to Use FFMI Calculator
1
Choose Your Units
Select metric for kilograms and centimetres or US customary for pounds and inches.
2
Enter Body Measurements
Provide current weight, height, and a body-fat percentage measured as consistently as possible.
3
Review the Live Results
Read FFMI, estimated lean mass, and the research-based height-normalized FFMI; results update automatically.
How the FFMI Calculator Works
The calculator first estimates fat-free mass by subtracting the body-fat share from total body weight. It then divides fat-free mass in kilograms by height in metres squared.
The normalized result adjusts FFMI toward a reference height of 1.80 metres using the 6.3 coefficient reported in the original Kouri study. Both FFMI values are rounded to two decimal places.
Lean mass = weight × (1 − body fat ÷ 100); FFMI = lean mass kg ÷ height m²; normalized FFMI = FFMI + 6.3 × (1.80 − height m)
Example
For 82 kg, 180 cm, and 15% body fat, lean mass is 82 × 0.85 = 69.7 kg. FFMI is 69.7 ÷ 1.80² = 21.51. At exactly 1.80 m, normalized FFMI is also 21.51.
FFMI Calculator Features
- Live FFMI, lean-mass, and normalized-FFMI results
- Metric and US customary unit conversion
- Original 6.3 height-normalization coefficient
- Visible formula, assumptions, and research limitations
Common Use Cases
Compare body-composition scenarios
Change weight or body-fat percentage to explore how a different lean-mass estimate changes FFMI.
Convert an existing body-fat estimate
Turn a measured or professionally estimated body-fat percentage into estimated lean mass and FFMI.
Limits and Important Notes
- FFMI is only as accurate as the entered body-fat estimate; consumer scales and field methods can vary substantially.
- Hydration, glycogen, recent food intake, and measurement technique can change weight or body-fat estimates.
- The height-normalization model came from a study of male athletes and should not be treated as a universal classification system.
- A particular FFMI value cannot diagnose health, determine training status, or prove performance-enhancing drug use.