FFMI Calculator: Fat-Free Mass Index & Body Recomp

Written by AdnanUpdated October 27, 2026Sources listed at the end

What FFMI measures

Fat-free mass index (FFMI) is like BMI, but it only counts your lean mass: muscle, bone, organs and water. Because fat is removed, it shows how muscular you are for your height. That makes it useful where BMI fails, for lifters and anyone trying to recompose.

The formula

Lean mass (kg) = weight × (1 − body fat % ÷ 100)

FFMI = lean mass ÷ height (m)²

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

Worked example

180 cm, 85 kg, 15% body fatLean mass = 85 × 0.85 = 72.3 kg. FFMI = 72.3 ÷ (1.80 × 1.80) = 22.3. At exactly 1.80 m the normalized value is the same, 22.3: well above average, typical of someone who has trained consistently for years. His fat mass index is 3.9.

165 cm woman, 62 kg, 25% body fatLean mass = 46.5 kg. FFMI = 17.1, normalized 18.0, in the range of a woman who trains regularly.

The natural limit

The best-known FFMI study, by Kouri and colleagues in 1995, measured 157 male athletes. Those who had never used anabolic steroids reached a normalized FFMI of up to about 25; values above that were mostly seen in steroid users. Treat 25 as a rough ceiling for drug-free men, not a hard rule.

Body recomposition

Body recomposition ("recomp") means losing fat and gaining muscle at the same time, so your weight may barely change while your shape does. It is most realistic for beginners, people returning to training, and people with more body fat to lose. Research reviews suggest trained lifters can recomp too, more slowly.

Eat around maintenance or a small deficit. Use the maintenance calculator.
Keep protein high: about 1.6–2.2 g per kg a day. Set it in the macro calculator, and see how much protein you need.
Lift with progressive overload three or more times a week.
Track FFMI, waist and strength, not just the scale. Re-measure body fat every 4 weeks with the body fat calculator.

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. PubMed 7496846
Barakat C, Pearson J, Escalante G, Campbell B, De Souza EO. Body recomposition: can trained individuals build muscle and lose fat at the same time? Strength Cond J. 2020;42(5):7–21.
Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20. PubMed 28642676

Frequently asked questions

What is a good FFMI?

For men, an FFMI of about 18–20 is typical for people who do not train, 20–22 is common for regular lifters, and 22–25 is very muscular. For women, about 14–17 is typical, and over 19 is very muscular. These are rough benchmarks, not medical categories.

What is the natural FFMI limit?

In a 1995 study of 157 male athletes, Kouri and colleagues found that men who had never used steroids topped out at a normalized FFMI of about 25. A few people exceed it naturally, but values well above 25 are uncommon without drugs.

Why is normalized FFMI different?

Taller people tend to have slightly higher FFMI values for the same build. Normalized FFMI adjusts every result to a height of 1.80 m: FFMI + 6.1 × (1.8 − height in metres). It makes people of different heights easier to compare.

Can I lose fat and build muscle at the same time?

Yes. This is body recomposition. It is most likely if you are new to lifting, returning after a break, or carrying more body fat, and it needs high protein and progressive strength training. Track it with FFMI and waist size rather than body weight.

How accurate is FFMI?

FFMI is only as accurate as your body fat estimate. A 3-point error in body fat changes FFMI by about 0.8 for an 80 kg, 178 cm man. Use the same body fat method each time and watch the trend.

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Rough FFMI benchmarks