Fat-Free Mass Index Calculator
Fat-Free Mass Index (FFMI)
Calculate fat-free mass and FFMI from height, weight and body-fat percentage. See formulas, a worked example and the limits of height adjustment. Fat-free mass is not muscle mass.
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StartAbout FFMI
FFMI is fat-free mass divided by height squared. Body-fat estimates affect the result; height adjustment is an approximate model. Fat-free mass includes muscle, bone, organs and body water; it is not a direct measurement of muscle mass.
- These are Moodji display bands, not validated population averages or diagnostic cutoffs. The female bands are illustrative and were not established by the cited male-athlete study. FFMI cannot establish steroid use or a personal natural limit.
- This calculator retains a height-adjustment coefficient of 6.1. The linked 1995 abstract reports 6.3; this version difference is disclosed rather than treated as a universal standard. The raw FFMI is also shown.
- Example: 70 kg, 175 cm and 20% body fat gives 56 kg fat-free mass, raw FFMI 18.29 and adjusted FFMI 18.59 (6.1 coefficient); displayed values round to one decimal.
About this tool
What is Fat-Free Mass Index Calculator?
FFMI is fat-free mass divided by height squared. Body-fat estimates affect the result; height adjustment is an approximate model. Fat-free mass includes muscle, bone, organs and body water; it is not a direct measurement of muscle mass.
What is it for?
Compare the calculated index and understand the assumptions behind it, without using it to diagnose health, drug use or training potential.
How to read your result
These are Moodji display bands, not validated population averages or diagnostic cutoffs. The female bands are illustrative and were not established by the cited male-athlete study. FFMI cannot establish steroid use or a personal natural limit.
Classification & Reference
| Male setting | Female setting | Display band |
|---|---|---|
| <18 | <14 | Lower range |
| 18–20 | 14–16 | Middle range |
| 20–22 | 16–18 | Elevated range |
| 22–24 | 18–20 | High range |
| ≥24 | ≥20 | Very high range |
Formula
Fat-free mass (kg) = weight (kg) × (1 − body fat (%) / 100)FFMI = fat-free mass (kg) / height (m)²Adjusted FFMI = FFMI + 6.1 × (1.8 − height (m))How FFMI is calculated
- Enter weight in kg, height in cm and body-fat percentage as a number, e.g. 20 for 20%.
- Fat-free mass (kg) = weight (kg) × (1 − body fat (%) / 100)
- FFMI = fat-free mass (kg) / height (m)²
- Adjusted FFMI = FFMI + 6.1 × (1.8 − height (m))
- Example: 70 kg, 175 cm and 20% body fat gives 56 kg fat-free mass, raw FFMI 18.29 and adjusted FFMI 18.59 (6.1 coefficient); displayed values round to one decimal.
- This calculator retains a height-adjustment coefficient of 6.1. The linked 1995 abstract reports 6.3; this version difference is disclosed rather than treated as a universal standard. The raw FFMI is also shown.
Frequently asked questions
Is fat-free mass the same as muscle mass?
Fat-free mass includes muscle, bone, organs and body water; it is not a direct measurement of muscle mass.
Does an FFMI above 25 prove steroid use?
No. The cited 1995 study examined 157 male athletes. Its observations do not establish a universal personal ceiling or prove drug use in an individual.
Are the female bands research-based norms?
No. The cited study does not validate these female display bands. They are illustrative groups in this tool, not a diagnosis or a measured population average.
Why does the height-adjustment coefficient differ?
This calculator retains a height-adjustment coefficient of 6.1. The linked 1995 abstract reports 6.3; this version difference is disclosed rather than treated as a universal standard. The raw FFMI is also shown.
Can I reproduce a calculation?
Example: 70 kg, 175 cm and 20% body fat gives 56 kg fat-free mass, raw FFMI 18.29 and adjusted FFMI 18.59 (6.1 coefficient); displayed values round to one decimal.