FFMI Calculator
This FFMI calculator compares your lean mass with your height, using your weight and body fat percentage.
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Field Notes that go deeper
The science behind the FFMI calculator
Show the formulas, method and sources
FFMI, the fat-free mass index, divides your lean mass by your height squared. A normalized version then adjusts for height. The tool finds lean mass from your weight and body fat percentage.
Formulas
Lean mass
Lean mass (kg) = weight (kg) x (1 - body fat % / 100)
FFMI
FFMI = lean mass (kg) / height (m)^2
Normalized FFMI
Normalized FFMI = FFMI + 6.3 x (1.80 - height (m))
How it works, step by step
- First, the calculator converts your height and weight to meters and kilograms.
- Then it subtracts the fat share you entered to find lean mass.
- Next, it divides lean mass by height squared.
- Finally, it adds the height adjustment, which is zero at 1.80 m.
Worked example
A man who is 190 cm tall with 80 kg of lean mass has an FFMI of 80 / 1.9^2 = 22.16, shown as 22.2. The normalized value then comes to 22.16 + 6.3 x (1.80 - 1.90) = 21.53, shown as 21.5.
Accuracy and limits
Kouri and colleagues defined the index and the 6.3 height adjustment in 1995. They studied 157 male athletes, 83 who had used anabolic-androgenic steroids and 74 who had not.
Among the nonusers, normalized values reached 25.0. Twenty Mr. America winners from 1939 to 1959 averaged 25.4. The authors called their findings preliminary.
Because the index depends on lean mass, an error in your body fat estimate carries straight through. A 2-point change in body fat at 80 kg moves lean mass by 1.6 kg.
- The sample was male athletes, so the figures say little about women or people who do not train.
- The 25.0 figure comes from one small study, so it works as a reference point only.
- The index cannot show where your lean mass sits or how strong you are.
Sources
- 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. Used for: The FFMI formula, the height adjustment and the sample it was studied in.
Sources and math last reviewed: .
Questions people ask
What is FFMI?
FFMI is the fat-free mass index. It divides your lean mass in kilograms by your height in meters, squared, so it describes how much lean tissue you carry for your height.
What is a good FFMI?
No single number counts as good. In a 1995 sample, male athletes who had not used steroids reached a normalized value of 25.0, but that came from one small study, so treat it as a reference point.
What is the difference between FFMI and BMI?
BMI counts all of your weight. FFMI counts only lean mass, so someone with more muscle and less fat can have a high BMI and a moderate FFMI.
Why is FFMI normalized?
Taller people tend to have larger raw values. The normalized value adds 6.3 x (1.80 - height in meters), which puts everyone on the scale of a 1.80 m person.
Where do I get my body fat percentage?
A scan gives one, and so do calipers and tape-measure methods. The body fat calculator gives a tape-measure estimate, and the result here changes with whichever number you enter.
How do I calculate FFMI by hand?
Multiply your weight by one minus your body fat fraction to get lean mass. Then divide by your height in meters, squared. For 100 kg at 20% body fat and 1.90 m, lean mass is 80 kg, so FFMI is 80 / 3.61 = 22.2.
These calculators give general estimates for adults and are not medical advice. For decisions about your own health, talk with a doctor or a registered dietitian. How we write and check things