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 weight, height, and body fat → Get FFMI, lean mass, and height-normalized results.
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.
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.
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
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.
Formula
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.
- When tracking a body-composition trend, use weight, height, and body-fat estimates measured consistently; compare repeated results instead of treating one FFMI value as a diagnosis or universal rating.
- There is no universal official FFMI pass/fail score; clinical, population, and athletic reference values answer different questions and are not interchangeable.
- 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.