FFMI Calculator
Lean mass for your height, in one number.
The equations were fitted separately for men and women, so they need one of the two. It is the body the formula describes, not an identity.
From a measurement, or estimated with the body fat calculator. FFMI is only as good as this number.
Fill in the fields and the answer appears here.
An estimate from a formula, not a measurement. It does not replace a doctor, a dietitian or a qualified trainer — least of all with a health condition, during pregnancy or breastfeeding, or under 18.
How this was worked out
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Guide: BMI without the fat2 min read
BMI without the fat
BMI divides weight by height squared and has no idea what the weight is. FFMI does the same sum with lean mass only — weight minus fat — and so answers a different question: how much muscle you carry for your height. It needs your body fat percentage; without a measurement, the body fat calculator estimates one with a tape.
The adjustment to 1.80 m
Taller people carry less lean mass per square metre of height, so raw FFMI flatters shorter people. The study that introduced the index, Kouri and colleagues (1995), added 6.1 × (1.8 − height) to bring everyone to 1.80 m. The calculator shows both, with the adjusted one first.
The famous 25, without the myth
In the same study, the highest adjusted FFMI among 83 male athletes who did not use steroids was 25.0. That is where the “natural limit” comes from. It is a fact about one group of men in one study, not a rule, a target or a verdict: the best use of the number is following your own lean mass over months. The study measured only men, so there is no matching value for women. Nothing you type is kept.
How we calculate
Fat-free mass index (1995)
lean mass = weight × (1 − body fat); FFMI = lean mass ÷ height²; adjusted FFMI = FFMI + 6.1 × (1.8 − height in m)
Source: Kouri EM, Pope HG Jr, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med. 1995;5(4):223-228.
Frequently asked questions
What is FFMI?
The fat-free mass index: your lean mass — everything that is not fat — divided by your height squared. It is BMI without the fat, which makes it a measure of how much muscle you carry for your height.
What is the adjusted FFMI?
FFMI plus 6.1 × (1.8 − your height in metres). Taller people carry less lean mass per square metre, so the adjustment brings everyone to 1.80 m and makes lifters of different heights comparable. It is the version the 1995 study used.
What is the natural limit of FFMI?
In the 1995 study by Kouri and colleagues, the highest adjusted FFMI among 83 drug-free male athletes was 25.0. That is where those athletes stopped, in one study of men, not a rule of nature, a target or a verdict.
Does FFMI work for women?
The number is computed the same way and tracks lean mass over time just as well. The study behind the reference values measured only men, so there is no matching figure to compare women against.
How accurate is it?
As accurate as the body fat you type in. A few points of error in body fat move the FFMI by a whole point, so use the same measurement method each time and watch the trend.