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FFMI calculator

Fat-free mass index tells you how much lean mass you carry for your height. Enter weight, height and body fat to see your FFMI, normalized FFMI and where it sits on the research scale.

Lean Mass Index

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Normalized FFMI–

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FFMI (raw)–

Lean body mass–

Fat mass–

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Bands are approximate references derived from published FFMI data (Kouri et al. 1995; Schutz et al. 2002), not diagnostic categories.

Plan a lean bulk → Estimate body fat

FFMI reference bands

Band	Men	Women	What it typically looks like

How FFMI is calculated

FFMI separates the two things BMI mixes together: fat and everything else. First lean body mass is computed from your weight and body-fat percentage, then it is divided by height squared.

Lean body mass (kg) = weight × (1 − body fat% / 100) FFMI = lean body mass / height(m)² Normalized FFMI = FFMI + 6.1 × (1.8 − height(m))

Why the "25" number is famous

In a 1995 study of 157 male athletes, Kouri and colleagues found that drug-free lifters topped out at a normalized FFMI of roughly 25, while many anabolic steroid users were well above it. It's a helpful benchmark for setting realistic expectations — not a rule your body is bound by.

Accuracy depends on body fat

Because FFMI is computed from body-fat percentage, any error there flows straight into the result: a 3-point body-fat error changes FFMI by about 0.7 for an average-height man. Track it over months with the same body-fat method for the most meaningful picture of muscle gain.

Frequently asked questions

What is FFMI?

Fat-Free Mass Index is your lean body mass (everything except fat) divided by height squared, in kg/m². It works like BMI but ignores fat, so it describes how much muscle and other lean tissue you carry for your height.

What is a good FFMI?

For men, values around 18–20 are typical of untrained to moderately trained people, 20–22 indicates clearly above-average muscularity, and 22–25 is seen in advanced, well-trained lifters. Women's values are roughly 3–4 points lower for comparable training status.

Is an FFMI of 25 the natural limit?

In Kouri et al. (1995), drug-free male athletes had a normalized FFMI up to about 25, while many steroid users exceeded it. It is a useful reference rather than a hard limit: a small number of drug-free individuals exceed 25, and body-fat estimation errors can easily shift FFMI by a point or more.

What is the normalized FFMI?

Taller people naturally have slightly higher FFMI values. The normalized FFMI adds 6.1 × (1.8 − height in metres) to adjust everyone to a reference height of 1.80 m, so people of different heights can be compared.

Sources & further reading

Kouri EM, Pope HG Jr, Katz DL, Oliva P (1995). Fat-free mass index in users and nonusers of anabolic-androgenic steroids . Clin J Sport Med 5(4):223–228 · doi:10.1097/00042752-199510000-00003
Schutz Y, Kyle UU, Pichard C (2002). Fat-free mass index and fat mass index percentiles in Caucasians aged 18–98 y . Int J Obes 26(7):953–960 · doi:10.1038/sj.ijo.0802037
VanItallie TB, Yang MU, Heymsfield SB, Funk RC, Boileau RA (1990). Height-normalized indices of the body's fat-free mass and fat mass: potentially useful indicators of nutritional status . Am J Clin Nutr 52(6):953–959 · doi:10.1093/ajcn/52.6.953