FFMI Calculator (Fat-Free Mass Index)
Measure your muscularity with the Fat-Free Mass Index, normalised for height.
How to use the ffmi calculator
- Choose units.
- Enter your weight, height and body-fat percentage.
- Click Calculate to see your FFMI and normalised FFMI.
FFMI and the natural limit
Research popularised the idea that a normalised FFMI near 25 marks the upper limit of natural muscularity. It is a guide, not a hard rule, but useful for setting realistic expectations.
Why FFMI beats BMI for lifters
FFMI measures fat-free mass relative to height, so unlike BMI it rewards muscle rather than penalising it. It answers a question BMI cannot: how muscular are you for your height, independent of body fat?
Interpreting your FFMI
Values around 18-20 are typical for untrained men, the low-to-mid 20s reflect years of dedicated training, and a normalised FFMI around 25 is often cited as the rough natural ceiling for men, though genetics shift this. Women's values run lower. Use it as a long-term progress marker, not a daily metric.
Frequently asked questions
What is a good FFMI?
Around 18–20 is average, 22–23 is very muscular, and roughly 25 is considered the natural ceiling for most drug-free lifters.
What does FFMI measure?
FFMI scales your fat-free (lean) mass to your height, giving a muscularity index that is independent of body fat — unlike BMI.
What is a good FFMI?
For men, the low 20s indicates a well-trained physique, while around 25 is often cited as the approximate natural limit. Women's values are lower for the same training status.
Can FFMI detect steroid use?
A very high normalised FFMI is sometimes used as a rough flag, but it is not proof. Genetics, measurement error, and body-fat estimates all affect the number.
How is FFMI different from BMI?
BMI uses total weight and cannot separate muscle from fat. FFMI uses fat-free mass, so it specifically reflects muscularity.
Related tools
Lean Body Mass Calculator
Estimate how much of your body weight is lean mass versus fat using the Boer formula.
Body Fat Calculator
Estimate your body-fat percentage using the U.S. Navy circumference method — just a tape measure required.
BMI Calculator
Calculate your Body Mass Index and see which WHO weight category it falls into.