FFMI Calculator
Enter your weight, body-fat percentage, and height to get your fat-free mass index (FFMI) and normalized FFMI. FFMI measures how much muscle you carry for your height, independent of body fat.
How to calculate ffmi
Fat-free mass index measures lean mass relative to height, much like BMI but excluding fat. First find your fat-free mass: weight times (1 minus your body-fat percentage). Convert it to kilograms and your height to metres, then divide the mass by your height squared. The normalized version adjusts the score to a reference height of 1.8 m (about 5 ft 11 in) so taller and shorter people can be compared fairly. FFMI is popular for gauging muscularity because, unlike BMI, it does not penalise a muscular build.
FFMI = fat-free mass (kg) / height (m)^2; normalized FFMI = FFMI + 6.1 x (1.8 - height in m)
Worked example
A man weighs 180 lb at 15% body fat and is 5 ft 10 in (70 in) tall.
- Fat-free mass: 180 lb x (1 - 0.15) = 153 lb, which is about 69.4 kg
- Height: 70 in is about 1.78 m
- FFMI: 69.4 / (1.78 x 1.78) = about 21.9
- Normalized FFMI: 21.9 + 6.1 x (1.8 - 1.78) = about 22.0
Result: An FFMI of about 22, in the typical range for a lean, fit adult male.
Frequently asked questions
What is a good FFMI?
For men, an FFMI around 18 to 20 is average, 20 to 22 is fit and athletic, and 22 to 25 indicates a high level of natural muscle. For women, the scale runs roughly 4 to 5 points lower. Values above about 25 are very rarely reached without performance-enhancing drugs.
What is the difference between FFMI and normalized FFMI?
Plain FFMI divides fat-free mass by height squared, so taller people tend to score slightly lower for the same build. Normalized FFMI adds an adjustment back to a 1.8 m reference height, making scores comparable across heights. Most published FFMI ranges refer to the normalized figure.
How is FFMI different from BMI?
BMI uses total body weight, so a muscular person can be labelled overweight. FFMI uses only fat-free (lean) mass, so it rewards muscle instead of penalising it. That is why FFMI is preferred for athletes and lifters, though it requires a body-fat estimate that BMI does not.
How do I find my body-fat percentage?
Common methods include skinfold calipers, bioelectrical impedance scales, and DEXA scans, in rough order of cost and accuracy. Any estimate carries some error, which flows through to your FFMI, so treat the result as a guide and track the trend over time rather than a single reading.