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FFMI Calculator

Find your fat-free mass index.

How it is calculated

The fat-free mass index compares your lean mass with your height. First the lean mass is found: FFM = weight × (1 − bodyfat ÷ 100), with weight in kg and body fat in percent. Then FFMI = FFM ÷ h² + 6.3 × (1.8 − h), with height h in metres (the form takes centimetres and divides by 100). The second term is the height normalisation from Kouri et al. (1995): it adds a small bonus for people shorter than 1.8 m and subtracts for taller ones. The result is rounded to one decimal. The tool does not classify the value; body-fat input is the weak point, since estimates from scales or calipers carry errors.

Worked example

Weight 80 kg, height 180 cm, body fat 15%. Lean mass: 80 × (1 − 0.15) = 68.0 kg. Height in metres: 1.80, so h² = 3.24. Raw index: 68 ÷ 3.24 = 20.99. The adjustment 6.3 × (1.8 − 1.8) is 0, because this person is exactly 1.8 m tall. The FFMI is 21.0, with 68.0 kg of fat-free mass.

Try this example →

Common mistakes

  • Entering height in metres or feet. The field expects centimetres; typing 1.8 would give an absurdly large index.
  • Entering body fat as a fraction (0.15) instead of a percent (15).
  • Using BMI-style total weight as lean mass. Only the fat-free part counts, so the body-fat figure matters a lot.
  • Trusting a rough body-fat estimate. A 3-point error in body fat shifts the FFMI by several tenths.

Sources

About this calculator

This calculator finds your Fat-Free Mass Index (FFMI) — your fat-free (lean) mass in kilograms divided by height in meters squared, the same idea as BMI but stripped of body fat. The FFMI it reports is the height-normalized version, which adjusts the score to what it would be at 1.8m so people of different heights can be compared fairly, and it also shows your lean mass in kilograms.

Bodybuilders, strength athletes and coaches use FFMI to track how much muscle someone is actually carrying rather than just total weight, and natural lifters use it as a rough benchmark since a normalized FFMI above roughly 25 is unusual without performance-enhancing drugs. It needs your weight, height and body fat percentage to work.

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  • Editorial team

    The result is the height-adjusted FFMI: the tool adds 6.3 times (1.8 minus your height in metres), which lifts the value for anyone shorter than 1.80 m and lowers it for taller lifters. Everything rests on the body fat percentage, and scales, calipers and visual estimates can disagree by several points, so use one consistent method when tracking progress. If your result looks off, post your inputs so the case can be looked at.

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