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.
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.
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.