How FFMI is worked out
Your lean mass is everything that isn't fat: muscle, bone, organs and water. FFMI is your lean mass in kilograms divided by your height in metres squared, the same idea as BMI but without the fat.
Taller people naturally score a little higher, so researchers use an adjusted FFMI that evens this out: it adds 6.1 × (1.8 − your height in metres). That is the number the calculator shows first, and the one the research below uses.
What the numbers mean
- Most people: in a study of more than 5,000 people, Schutz and colleagues (2002) found FFMI was 16.7 to 19.8 for men and 14.6 to 16.8 for women of a healthy weight. Years of good training move you above that.
- Drug-free lifters: in 1995, Kouri, Pope and colleagues measured 157 male athletes, some of whom used anabolic steroids. The drug-free men topped out at an adjusted FFMI of about 25, while many of the steroid users were above it.
Treat 25 as a rough guide, not a hard limit. It comes from one study of men, a few genetically gifted drug-free athletes go a little above it, and there is much less research on women, whose values are lower. FFMI can't tell whether a particular person uses drugs, and neither can a photo.
Get an accurate result
FFMI is only as good as the body fat figure you put in. Most quick methods are a few percentage points off, and a body fat estimate 3 points too low raises your FFMI by close to 1. Use the same method each time, such as the tape measure body fat calculator, and watch the trend rather than a single result.
Next steps
If your FFMI is well below 25, you have plenty of room to grow naturally. Read how much muscle you can build naturally and how fast to gain weight on a lean bulk, or apply for coaching for a training and nutrition plan built for the next stage.
General guidance for adults, not medical advice. It is not suitable during pregnancy.