FFMI Calculator
Calculate your fat-free mass index (FFMI) — enter your height, weight and body-fat percentage to get your FFMI and the height-normalized FFMI.
Created and reviewed by Christoph Ballmer For general information only — not medical advice. FFMI estimates muscularity from your fat-free mass and height; its accuracy depends on a correct body-fat percentage, and the often-cited “natural limit” around 25 is a population observation, not a hard rule. Talk to a doctor or qualified professional about body composition and health.
How FFMI is calculated
The fat-free mass index (FFMI) measures how much lean mass you carry for your height — a better gauge of muscularity than BMI. First find your fat-free mass: weight × (1 − body-fat %). Then divide by your height in meters squared. The normalized FFMI adds a small height adjustment so tall and short people can be compared fairly. Enter your height, weight and body-fat percentage above — the calculator handles the unit conversions.
FFMI = fat-free mass (kg) ÷ height (m)², normalized = FFMI + 6.1 × (1.8 − height m)
For example, a 180 lb person at 5′10″ with 15% body fat has about 153 lb (69.4 kg) of fat-free mass and a normalized FFMI of roughly 22 — in the “very muscular” range.
FFMI ranges
| FFMI (men) | Interpretation |
|---|---|
| 18–20 | Average |
| 20–22 | Fit |
| 22–25 | Very muscular |
| ~25 | Often cited as the natural ceiling |
These are general ranges (a few points lower for women), and the result depends heavily on an accurate body-fat figure — measure that with the body fat calculator. FFMI is for general information, not medical advice.
Frequently asked questions
How is FFMI calculated?
First find your fat-free mass: weight × (1 − body-fat%). Then FFMI = fat-free mass (kg) ÷ height (m)². The normalized FFMI adds 6.1 × (1.8 − height in m) to adjust for height. The calculator converts US units for you and shows both numbers.
What is a good FFMI?
For men, roughly 18–20 is average, 20–22 is fit, and 22–25 is very muscular; the often-cited natural ceiling is around 25 (a few points lower for women). These are general ranges — your FFMI depends heavily on an accurate body-fat figure.
What is the difference between FFMI and BMI?
BMI uses only height and weight, so a muscular person can read as “overweight.” FFMI uses your fat-free (mostly muscle) mass instead, so it reflects muscularity rather than total weight. That makes FFMI more useful for lifters, where BMI can be misleading.