Fat-Free Mass Index (FFMI) Calculator
Find your FFMI from weight, height and body fat.
Results update as you type.
This calculator provides estimates based on population research. Results are not medical advice. Consult a qualified healthcare provider before making health or nutrition decisions.
How it works
The fat-free mass index, or FFMI, measures how much lean mass you carry relative to your height, and this calculator computes it. You enter your weight, height, and body-fat percentage, and it returns your fat-free mass, your FFMI, and a height-adjusted FFMI. Unlike BMI, which cannot distinguish muscle from fat, FFMI isolates lean mass, making it a better indicator of muscularity. It is calculated by first finding your fat-free mass, your weight minus your body fat, then dividing by your height in meters squared, just as BMI uses total weight. The adjusted version normalizes the result to a standard height so that taller and shorter people can be compared fairly. Typical FFMI values run from about 18 for an average untrained person to the low 20s for well-trained athletes. A frequently cited figure suggests a natural upper limit around 25 for men, above which achieving the result without performance-enhancing drugs becomes very unlikely, though genetics create individual variation. FFMI is useful for tracking muscle gain over time, comparing your muscularity to norms, and setting realistic goals. Its accuracy depends entirely on the body-fat percentage you enter, so use the most reliable measurement available. Enter your weight, height, and body fat to calculate your FFMI.
FFMI = fat-free mass (kg) / height (m)² ; FFM = weight × (1 − body fat%)
Fat-free mass is your weight minus your fat, calculated as weight times one minus your body-fat fraction. Dividing that by your height in meters squared gives the fat-free mass index, analogous to BMI but for lean mass. The adjusted FFMI adds a correction of 6.1 times (1.8 − height in meters) to normalize for stature.
Source:Fat-free mass index (Kouri et al.)
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter body weight, height and body fat.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
FFMI updates instantly as you type — no button to press.
Frequently asked questions
What is FFMI and how is it different from BMI?
FFMI, the fat-free mass index, measures lean mass relative to height, while BMI measures total weight relative to height. Because BMI cannot separate muscle from fat, a muscular person may register as overweight. FFMI isolates fat-free mass, so it better reflects muscularity and is favored by athletes and those tracking muscle gain.
How is FFMI calculated?
First find your fat-free mass by multiplying your weight by one minus your body-fat fraction. Then divide that lean mass by your height in meters squared, the same denominator BMI uses. The adjusted FFMI adds a small correction based on height so people of different statures can be compared on a common scale.
What is a good FFMI?
Values typically range from about 18 for an untrained average person to the low 20s for well-trained athletes. Higher numbers indicate more muscularity. What counts as good depends on your goals and starting point; tracking your own FFMI over time to see lean-mass changes is often more useful than comparing to a single benchmark.
Is there a natural FFMI limit?
A widely cited analysis suggested a natural ceiling around 25 for men, above which reaching the value without performance-enhancing drugs is very unlikely. This is a general guideline, not an absolute rule, since genetics, frame size, and measurement error create individual variation. Women generally have lower FFMI values due to differences in body composition.
Why does the body-fat percentage matter so much?
FFMI depends directly on fat-free mass, which is derived from your body-fat percentage. If the body-fat figure is inaccurate, the resulting FFMI will be off too. For the most reliable result, use the best body-fat measurement available, such as DEXA or skinfold calipers by a trained tester, rather than a rough estimate.