About the FFMI Calculator
This FFMI calculator measures how much lean mass you carry for your height. Fat-free mass index is like BMI but uses only fat-free mass — muscle, bone, organs and water — so it separates a muscular lifter from someone who is simply heavy. You need your weight, height and an estimate of body fat percentage.
It is popular with bodybuilders, strength athletes and anyone tracking a recomposition, because FFMI keeps rising as you add muscle even when the scale barely moves. The normalized FFMI adjusts the score to a height of 1.8 m so tall and short people can be compared fairly; a well-known 1995 study by Kouri and colleagues found drug-free male athletes rarely exceeded a normalized FFMI of about 25.
Accuracy depends on your body fat estimate: a 3-point error in body fat shifts FFMI by roughly 0.7. Use a consistent method (DEXA, calipers or a tape formula) and track the trend rather than a single reading.
With the default inputs, the ffmi is 21 kg/m². Change any value above to recalculate instantly.
How to use the ffmi calculator
- 1Select your sex and choose metric or imperial units.
- 2Enter your weight and height.
- 3Enter your body fat percentage from the most reliable method you have.
- 4Read your FFMI, normalized FFMI and rating.
- 5Re-check every few weeks to track muscle gain during a bulk or recomposition.
Formula and method
Fat-free mass is total weight in kilograms minus fat mass (weight × body fat %). Dividing by height in metres squared gives FFMI in kg/m², the same shape as BMI.
Because taller people tend to have slightly lower FFMI for the same muscularity, Kouri et al. (1995) proposed adding 6.1 × (1.8 − height in metres) to normalize every score to a height of 1.8 m. The ratings used here are approximate community benchmarks; in the original study most drug-free male athletes had normalized FFMI below 25. The lean-mass target inverts the normalized formula for a score of 25.
- FFMI
- Fat-free mass index, kg/m²
- BF%
- Body fat as a fraction
- height
- Height in metres
Worked examples
180 cm, 80 kg man at 15% body fat
Fat-free mass is 80 × 0.85 = 68 kg. 68 ÷ 1.8² = 21.0 — and because he is exactly 1.8 m, normalized FFMI is the same. That rates as above average, about 13 kg of lean mass below the FFMI-25 ceiling.
Imperial: 5 ft 8 in, 190 lb at 12%
190 lb is 86.18 kg, so lean mass is 75.84 kg. Height is 1.727 m, giving FFMI 75.84 ÷ 2.984 = 25.4, and normalized 25.4 + 6.1 × (1.8 − 1.727) = 25.9 — above the typical drug-free ceiling.
Woman, 165 cm, 62 kg at 24% body fat
Lean mass is 62 × 0.76 = 47.1 kg. 47.1 ÷ 1.65² = 17.3, and normalizing to 1.8 m adds 6.1 × 0.15 = 0.9, giving 18.2 — an excellent level of muscularity for a woman.
Frequently asked questions
What is a good FFMI?+
For men, a normalized FFMI of 18–20 is average, 20–22 above average and 22–25 very muscular. For women, around 15–17 is average and 18–21 very muscular. Untrained people usually sit at the lower end.
What is the natural FFMI limit?+
In Kouri et al.’s 1995 study of 157 male athletes, drug-free lifters rarely exceeded a normalized FFMI of about 25, while many steroid users did. A few genetically gifted natural athletes exceed it, so it is a guideline rather than a hard limit.
How is FFMI different from BMI?+
BMI uses total weight, so a lean, muscular person can be classified as overweight. FFMI removes fat mass first, so it reflects muscularity. Together, FFMI and body fat percentage describe body composition far better than BMI.
Why normalize FFMI to 1.8 metres?+
Lean mass does not scale exactly with height squared, so taller people score slightly lower for the same build. Adding 6.1 × (1.8 − height) corrects this and allows fair comparison between people of different heights.
How accurate is FFMI?+
It is only as accurate as your body fat estimate. Consumer scales and tape formulas can be off by 3–5 percentage points, which changes FFMI by about 0.7–1.2. DEXA gives the most reliable body fat for this purpose.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.