FFMI Calculator
This free FFMI calculator finds your Fat-Free Mass Index — a measure of how much muscle you carry relative to your height. Unlike BMI, which ignores body composition, FFMI focuses on lean mass, making it a popular way for athletes and lifters to gauge muscularity and progress. Enter your weight, height, and body fat percentage, and the calculator returns your FFMI and normalized FFMI.
How to Use the FFMI Calculator
- Enter your weight and height.
- Enter your body fat percentage.
- Calculate — see your FFMI and normalized FFMI.
The FFMI Formula
First find your fat-free mass, then divide by height squared:
Fat-Free Mass = Weight × (1 − Body Fat % ÷ 100)
FFMI = Fat-Free Mass (kg) ÷ Height (m)²
A normalized FFMI adjusts the value to a standard height of 1.8 m for fairer comparison between people of different heights.
FFMI Ranges
| FFMI (men) | Interpretation |
|---|---|
| 18–20 | Average |
| 20–22 | Above average, fit |
| 22–23 | Very muscular |
| ~25 | Often cited as the natural limit |
Women's FFMI values run a few points lower. An FFMI around 25 is frequently cited as the upper limit achievable naturally, though individual genetics vary.
FFMI vs BMI
BMI uses only weight and height, so a muscular person can register as "overweight" despite low body fat. FFMI corrects for this by measuring lean mass specifically, giving athletes and lifters a far more meaningful number for tracking muscle development.
Note: FFMI depends on an accurate body fat measurement. This is a fitness metric, not a medical diagnosis.
Frequently Asked Questions
What is FFMI?
Fat-Free Mass Index measures your lean (non-fat) body mass relative to your height, indicating how muscular you are independent of body fat.
How do you calculate FFMI?
Find your fat-free mass (weight × (1 − body fat % ÷ 100)), then divide by your height in meters squared.
What is a good FFMI?
For men, 20–22 is fit and above average, 22–23 is very muscular, and around 25 is often cited as the natural limit. Women's values are a few points lower.
How is FFMI different from BMI?
BMI uses total weight and can misclassify muscular people as overweight, while FFMI measures lean mass specifically, making it more useful for athletes.
Is this FFMI calculator free?
Yes — it is completely free, requires no signup, and gives your FFMI and normalized FFMI.