FitCalculationLean mass (kg) = weight (kg) × (1 − body fat % ÷ 100)
FFMI Calculator
Calculate your Fat-Free Mass Index from height, weight, and body fat percentage. Shows both raw and height-adjusted FFMI.
Fat-free mass index (FFMI) measures how much lean mass you carry for your height. Find out what your FFMI is in seconds: enter your height, weight and body fat percentage and this calculator shows both your raw FFMI and your normalized FFMI, which adjusts for height. Your numbers stay in your browser.
For generally healthy adults. Not medical advice. FFMI depends on your body fat estimate, which can be off by several percentage points, so treat the result as a rough guide.
What this calculates
Lean mass is divided by height squared to get FFMI, then a height-correction term is added so shorter and taller people can be compared on the same scale.
How to calculate FFMI
FFMI = lean mass (kg) ÷ height (m)²
Normalized FFMI = FFMI + 6.1 × (1.8 − height in m)
All the maths runs in metric. Imperial inputs — height in feet and inches and weight in pounds — are converted to centimeters and kilograms before these formulas are applied, so the result is the same in either unit system. The height correction uses a fixed reference of 1.8 m with a 6.1 coefficient, which is what makes the normalized value comparable across different statures.
FFMI depends on your body fat percentage, which this calculator does not measure itself. If you don't already have one, the body fat calculator estimates it from tape measurements, and the lean body mass calculator splits your weight into lean and fat mass the same way.
Worked examples
Man, 180 cm, 80 kg, 15% body fat
| Lean mass | 68.0 kg |
|---|---|
| FFMI | 21.0 |
| Normalized FFMI | 21.0 (at 1.80 m, no adjustment) |
Man, 190 cm, 95 kg, 12% body fat
| Lean mass | 83.6 kg |
|---|---|
| FFMI | 23.2 |
| Normalized FFMI | 22.5 |
Woman, 165 cm, 62 kg, 24% body fat
| Lean mass | 47.1 kg |
|---|---|
| FFMI | 17.3 |
| Normalized FFMI | 18.2 |
What is a good FFMI?
These are informal rules of thumb for men, not medical categories, and not a target to chase:
- Below 18below average
- 18 to 20average
- 20 to 22above average
- 22 to 23excellent
- 23 to 25superior
- Above 25rare without performance-enhancing drugs
Reference ranges for women are lower and less well studied, so use them with extra caution.
To build or hold lean mass, a higher protein target and enough daily calories help. The protein calculator sets a gram target from your weight, the TDEE calculator sets your maintenance calories, and the body recomposition calculator combines both into a plan for gaining muscle while losing fat.
FFMI vs BMI
BMI divides your total weight by your height squared, so it cannot tell muscle from fat: a muscular person can have a high BMI while carrying little body fat. FFMI removes fat from the calculation, dividing lean mass by height squared, so it isolates muscle — but only as far back as your body fat estimate is accurate.
For the screening number that compares your weight to your height, use the BMI calculator. For the body fat percentage that FFMI depends on, use the body fat calculator.
The 25 limit: what it does and doesn't mean
The oft-cited 25 FFMI figure comes from Kouri et al. (1995), a cross-sectional study of male bodybuilders using or not using anabolic-androgenic steroids. It was an observation, not a medical threshold.
Some natural athletes in that study scored above 25, and several factors move an FFMI result by more than the headline number: your body fat estimate, the method behind it, and ordinary measurement error. A tape-based body fat figure can be off by several percentage points, and that error flows straight into lean mass and FFMI.
Do not treat any single FFMI as proof of drug use. It is an estimate built from an estimate, useful for context, not for judgment.
Frequently asked questions
What is my FFMI?
Enter your height, weight and body fat percentage in the calculator above and it returns your FFMI and your normalized FFMI. For example, a man who is 180 cm, 80 kg and 15% body fat has an FFMI of about 21.0. The result is only as accurate as your body fat estimate.
What is FFMI?
FFMI stands for fat-free mass index. It divides your lean mass (everything except body fat) by your height squared, a bit like BMI but without counting fat. It's mainly used to describe muscularity relative to height.
How do I calculate FFMI?
First work out lean mass: weight × (1 − body fat percentage ÷ 100). Then divide by height in metres squared. A man who is 180 cm, 80 kg and 15% body fat has 68 kg of lean mass, and 68 ÷ 1.8² gives an FFMI of 21.0. The calculator above does this for you and also shows the normalized value.
What is a good FFMI?
For men, an FFMI of roughly 18 to 20 is typical, 20 to 22 is above average, and 22 to 25 is well-muscled. These are informal rules of thumb, not medical categories. Reference ranges for women are lower and less well studied, so use them with caution.
What is normalized FFMI?
Normalized FFMI adjusts your FFMI to a standard height of 1.8 m (about 5 ft 11 in) using this formula: FFMI + 6.1 × (1.8 − height in metres). It makes results more comparable between very tall and very short people. A 190 cm man with a raw FFMI of 23.2 has a normalized FFMI of 22.5.
What is the natural limit for FFMI?
A frequently quoted figure is about 25, based on a 1995 study of male athletes. It's a rough guide, not a hard cutoff. Some natural athletes score higher, and body fat estimates can shift the result by a lot. No single FFMI proves whether someone has used performance-enhancing drugs.
How accurate is FFMI?
Only as accurate as your body fat measurement. A few percentage points of error in body fat can move your FFMI by about a point. Methods like DEXA are more reliable than calipers or smart scales, and tape-measure estimates are rougher still. Retest using the same method to track change.
What is the difference between FFMI and BMI?
BMI divides total weight by height squared, so it can't tell muscle from fat. A muscular person can have a high BMI but a healthy body fat level. FFMI removes fat from the calculation, so it focuses on lean mass, but it needs a body fat estimate that BMI doesn't.
Sources and last reviewed
Last reviewed: October 2026
- VanItallie TB et al. (1990), "Height-normalized indices of the body's fat-free mass and fat mass", Am J Clin Nutr 52(6):953-959
Used for: Height-normalized indices of fat-free mass.
- 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
Used for: Fat-free mass index and the reference range observed in male athletes.
- Schutz Y, Kyle UUG, 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
Used for: Fat-free mass and fat mass index percentiles across age.