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Fat-free mass index

FFMI calculator

FFMI (fat-free mass index) is fat-free mass divided by height squared. In young Swiss adults, the median was 18.9 for men and 15.4 for women.

Source: Schutz et al., 2002

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The basics

What your FFMI means

Fat-free mass = weight × (1 - body fat % / 100)

FFMI = fat-free mass (kg) / height (m)²

Fat-free mass is everything that is not fat: muscle, but also bone and water. At 80 kg, 1.80 m and 15% body fat, it is 68.0 kg, and FFMI is 21.0.

FFMI plus fat mass index (FMI) equals BMI, so FFMI can separate two people with the same BMI. At that height and weight, 25% body fat gives an FFMI of 18.5.

People with more fat mass tend to carry more fat-free mass, so read FFMI next to your body fat %.

The FMI class in the result shows how common a level is (Kelly 2009), not disease risk.

Source: VanItallie et al., 1990, Kelly et al., 2009, Trexler et al., 2017

Percentiles

FFMI by age and sex

FFMI in kg/m². The 50th percentile is the median: half of each group sat below it.

Men
Age5th25th50th75th95th
Ages 18 to 3416.818.018.919.821.1
Ages 35 to 5417.218.319.220.121.7
Ages 55 to 7417.018.419.420.322.1
Ages 75 and over16.617.618.519.421.2
Women
Age5th25th50th75th95th
Ages 18 to 3413.814.715.416.217.6
Ages 35 to 5414.415.315.916.718.0
Ages 55 to 7414.115.416.217.419.0
Ages 75 and over12.914.715.917.018.7

From 5,635 apparently healthy Swiss adults, not randomly selected, measured by bioimpedance.

Source: Schutz et al., 2002

Source: Kelly et al., 2009, Kim et al., 2011, Currier et al., 2019, Trexler et al., 2017, Blue et al., 2019, Harty et al., 2019, Cederholm et al., 2015 (ESPEN)

Height adjustment

Normalized FFMI

Normalized FFMI = FFMI + 6.1 × (1.8 - height in m)

Kouri and colleagues added this in 1995 because taller athletes appeared to score higher at similar muscularity. It adjusts FFMI to a height of 1.80 m. It came from male athletes, so it is shown for men only.

Compare raw FFMI with the percentile tables. Use normalized FFMI only next to the 25.0 figure below.

The abstract prints 6.3, but its results use 6.1, a gap of at most 0.05 points from 1.55 m to 2.05 m.

Source: Kouri et al., 1995

The 25 figure

Is 25 the natural limit?

  • 25.0

    The highest normalized FFMI among 74 male athletes who reported no steroid use and had negative urine tests, in one 1995 study.

  • 23.0%

    Of 235 college football players were above 25 on the same formula in a later study. The study ran no drug tests of its own, though NCAA athletes face random testing. The players were heavier and carried more body fat than the 1995 group.

25.0 is the ceiling seen in that one sample, not a proven limit. The authors called the findings preliminary, said rare individuals may exceed it, and warned that the formula may not suit people with higher body fat.

FFMI alone cannot show steroid use. The same authors, who suggested it as a first screen, say so themselves.

The study covered men only, so the figure does not apply to women.

Source: Kouri et al., 1995, Trexler et al., 2017

Body fat input

How body fat moves FFMI

Each body fat point moves FFMI by BMI / 100, about 0.25 points at a BMI of 25. Results vary by method and calibration, so use the same method each time you compare.

Source: Kelly et al., 2009

Questions

FFMI, answered

  • What is a good FFMI?

    There is no official cut-off, so compare with people your age and sex. In healthy Swiss adults aged 18 to 34, the 95th percentile was 21.1 for men and 17.6 for women.

  • What is a normal FFMI for women?

    In healthy Swiss women, the median ran from 15.4 at ages 18 to 34 to 16.2 at ages 55 to 74.

  • How do I get my FFMI without a body fat percentage?

    You need a body fat estimate first. Measure with a tape or scan a photo, then enter the number here.

  • Is lean body mass the same as fat-free mass?

    In everyday use, yes: both mean your weight minus your fat. DXA reports can list bone separately, so their lean mass figure can be lower.

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