Home / Glossary / FFMI (Fat-Free Mass Index)

Biomarkers

FFMI — fat-free mass index

Q: Why is FFMI better than BMI?

BMI does not distinguish fat from muscle, so it may wrongly classify a muscular person as "overweight". FFMI takes into account fat-free mass specifically and shows whether a person has enough muscle relative to height.

Q: What FFMI is considered normal?

Roughly 18–22 kg/m² in men and 15–18 in women. Values below 18 (men) and 15 (women) indicate a deficit of muscle mass, while through natural training athletes can exceed 22–23.

Q: Can FFMI be used to suspect sarcopenia?

Yes, a low FFMI is one guide to a deficit of muscle mass. But for a diagnosis of sarcopenia muscle strength (for example, grip strength) and function matter too, not only mass. FFMI is best assessed together with the fat percentage.

Fat-free mass / height²

FFMI — the body's fat-free mass index, assessing muscle

FFMI (fat-free mass index) is fat-free mass divided by height squared. In meaning it is a "BMI for muscle": it shows whether a person has enough fat-free (mainly muscle) mass relative to height.

FFMI solves the main problem of BMI, which does not distinguish fat from muscle. A low FFMI signals a deficit of muscle (a risk of sarcopenia), a high one — well-developed musculature.

Reference ranges

FFMI = fat-free mass (kg) / height² (m²); approximate values:

Men — normal	≈ 18 – 22 kg/m²
Women — normal	≈ 15 – 18 kg/m²
Low muscle mass	men < 18, women < 15
Athletes	can naturally exceed 22–23

Important: FFMI depends little on height, so it is suitable for comparing people of different builds. The limits are approximate and depend on the body-composition measurement method.

What an elevated level means

A high FFMI means well-developed fat-free (muscle) mass — a favorable sign for strength, metabolism and bone health. Through natural training men usually reach a ceiling of about 22–25 kg/m².

Very high FFMI values are not harmful in themselves if achieved without anabolic drugs.

What a low level means

A low FFMI (men < 18, women < 15) indicates a deficit of muscle mass. It is a risk factor for weakness, metabolic disturbances and, in old age, sarcopenia.

A low FFMI can also hide behind a normal weight — if there is little muscle and a lot of fat. So FFMI is assessed together with the fat percentage.

How the test is done

To calculate FFMI, body composition is first measured (bioimpedance or DEXA) and fat-free mass obtained, then it is divided by height in meters squared.

FFMI is interpreted together with the fat mass index: together they give a full picture — whether there is enough muscle and whether fat is excessive.

What affects the value

Strength training and protein — raise FFMI.
Age — lowers FFMI (muscle loss).
The body-composition measurement method — affects the result.
Hydration — affects the bioimpedance estimate of fat-free mass.
Sex — FFMI is higher in men.
Immobility — lowers it quickly.

Assess body composition

Calculate your fat-free mass and compare it with BMI:

Body Composition Body fat, muscle mass (FFMI, SMM, SMI), body shape, and ABSI — all in one Open Body Mass Index (BMI) BMI and BMI Prime, WHO norms, waist-based risk, and the link to biological age Open

Frequently asked questions

Why is FFMI better than BMI?

BMI does not distinguish fat from muscle, so it may wrongly classify a muscular person as "overweight". FFMI takes into account fat-free mass specifically and shows whether a person has enough muscle relative to height.

What FFMI is considered normal?

Roughly 18–22 kg/m² in men and 15–18 in women. Values below 18 (men) and 15 (women) indicate a deficit of muscle mass, while through natural training athletes can exceed 22–23.

Can FFMI be used to suspect sarcopenia?

Yes, a low FFMI is one guide to a deficit of muscle mass. But for a diagnosis of sarcopenia muscle strength (for example, grip strength) and function matter too, not only mass. FFMI is best assessed together with the fat percentage.

Sources

info

This content is educational and does not replace consultation with a physician. Reference ranges may vary depending on the laboratory and method — rely on the ranges stated on your own test report.

← All glossary terms