FFMI Calculator
An 80 kg adult at 180 cm and 15% body fat has about 68 kg of lean mass and an FFMI of 21.0. This FFMI calculator estimates fat-free mass index from weight, height, and body fat percentage. It also shows lean mass and a normalized FFMI that adjusts the score to a 1.8 m reference height for rough adult comparison.
Quick answer
FFMI uses lean mass, not total body weight alone.
What this tells you
- •FFMI uses lean mass, not total body weight alone.
- •Lean mass here is your body weight multiplied by 1 minus body fat percentage as a decimal.
- •Normalized FFMI adjusts the score to a 1.8 m reference height.
- •The result is a comparison estimate, not a diagnosis or a performance grade.
How to Use
- 1Enter your current body weight in kilograms.
- 2Enter your height in centimeters.
- 3Enter your best body fat percentage estimate.
- 4Calculate to see lean mass, raw FFMI, and normalized FFMI.
- 5Use the result as a reference point, then compare it with consistent measurements over time.
How It Works
Formula
Lean mass = weight x (1 - body fat % / 100)
FFMI = lean mass / height (m)^2
Normalized FFMI = FFMI + 6.1 x (1.8 - height in m)First convert body fat percentage into a lean-mass fraction, then multiply that by body weight to estimate lean mass in kilograms. FFMI divides that lean mass by height in meters squared, similar to BMI but using fat-free mass. The normalized version adjusts the score to a 1.8 meter reference height, which is common in FFMI comparisons, but that adjustment is still only a rough comparison tool.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Adult at the 1.8 m reference height
Lean mass is 80 x 0.85 = 68 kg. FFMI is 68 divided by 1.8 squared, which rounds to 21.0. Because height is already 1.8 m, the normalized score stays the same.
Shorter adult with a small upward normalization
Lean mass is 70 x 0.82 = 57.4 kg. FFMI is 57.4 divided by 1.75 squared, which rounds to 18.7. The normalized score adds a small height adjustment because 1.75 m is below the 1.8 m reference.
Common mistakes
- Entering pounds as kilograms or inches as centimeters
- Treating a rough body fat estimate as exact, especially from a single smart-scale reading
- Comparing normalized FFMI tables without checking whether they were built on men, women, or mixed samples
- Using FFMI to judge health, athletic potential, or drug use from one number alone
Limitations
FFMI depends heavily on the body fat percentage you enter, so small errors in body fat can move lean mass and FFMI more than most people expect. The normalized formula shown here adjusts scores to a 1.8 m reference height, which is common in adult FFMI discussions, especially in physique-focused and male comparison contexts. It does not account for age, sex, frame size, hydration, edema, ethnicity, pregnancy, growth in children or teens, or how body fat was measured.