Comprehensive Calculator Guide
The fat-free mass index (FFMI) is like BMI but uses your weight without fat, so it measures muscle for your height rather than total weight. A man of 80 kg and 180 cm with 15% body fat has 68 kg of fat-free mass and an FFMI of about 21. Lifters use it because BMI mixes muscle with fat.
Formula and reading
FFMI = weight × (1 − body fat) ÷ height². The adjusted index adds 6.1 × (1.8 − height in m) to correct for height; at 1.80 m the two match.
In the study that introduced the adjusted index (Kouri and colleagues, 1995), men who had not used steroids rarely exceeded about 25. Results depend on your body fat estimate, so track changes measured the same way.
How to Use
- 01Enter weight and height.
- 02Enter body fat percentage.
- 03Read fat-free mass, FFMI and adjusted FFMI.
Formula Used
FFMI = fat-free mass ÷ height² | Adjusted = FFMI + 6.1 × (1.8 − height)Practical Examples
Example 1
80 kg, 180 cm, 15%: FFMI 21.0.
Example 2
70 kg, 170 cm, 20%: FFMI 19.4, adjusted 20.0.
Important Tips
- Measure body fat the same way each time.
Common Mistakes to Avoid
- Trusting the number with a rough body fat guess.
Frequently Asked Questions
- What is FFMI?
- Fat-free mass divided by height squared.
- How is it different from BMI?
- It leaves fat out.
- What counts as high?
- Values near 25 in men are rare without steroids, per the original study.