FFMI calculator
FFMI (fat-free mass index) is like BMI for muscle: it measures how much lean mass you carry for your height, ignoring fat. Enter your height, weight and body fat percentage to get your FFMI, the height-adjusted version, and your lean body mass.
How FFMI is calculated
Lean body mass = weight × (1 − body fat %). FFMI = lean mass in kg ÷ height in metres squared. The adjusted FFMI adds 6.1 × (1.8 − height in m), which corrects for taller people naturally scoring higher. This is the version most comparisons use.
Example: 80 kg at 15% body fat and 1.80 m gives 68 kg of lean mass and an FFMI of 21.0.
What counts as a high FFMI?
Most untrained men fall around 18–20 and most untrained women around 14–17. Years of consistent training typically push men into the 21–23 range.
In a 1995 study of strength athletes, Kouri and colleagues found that men who had never used anabolic steroids topped out at an adjusted FFMI of about 25. That figure is often quoted as a 'natural limit'. It's a useful reference, not a hard rule — a few people exceed it naturally, and body fat errors shift the result.
Why FFMI beats BMI for people who train
BMI can't tell muscle from fat, so a muscular person and a person with high body fat can share the same BMI. FFMI removes fat from the equation, which makes it a better way to track whether training is adding muscle — as long as the body fat estimate is measured the same way each time.
Track lean mass, not just weight
Trainr estimates body fat from two photos and charts your lean mass and measurements over time, so you can see muscle being built while the scale stays flat. The first scan is free.
Track your lean mass — freeCommon questions
What is a good FFMI?
For men, 20–22 is above average and 22–23 excellent; for women, roughly 16–17.5 is above average. Most people who train consistently land there after a few years.
Is an FFMI of 25 natural?
In Kouri's 1995 study, drug-free men topped out near 25. Some genetically gifted people exceed it naturally, but it's rare.
How is lean body mass different from muscle mass?
Lean mass is everything that isn't fat: muscle, bone, organs and water. Muscle is the largest part of it, and the part that changes with training.
How accurate is FFMI?
It inherits the error of your body fat number. A 3-point error in body fat moves FFMI by about 0.7. Use the same body fat method each time.
FFMI tells you how much muscle you carry for your height; measured regularly, it shows whether training is working.
Sources
- Kouri EM, Pope HG Jr, Katz DL, Oliva P (1995). Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clinical Journal of Sport Medicine. https://pubmed.ncbi.nlm.nih.gov/7496846/
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Trainr is a wellness tool, not a medical device. These calculators give estimates for self-tracking, not a diagnosis. For medical questions, talk to a professional.