Fat Free Mass Index (FFMI) Calculator

Index variables

The FFMI uses three variables to provide an index score that provides information on the natural or steroid muscle mass build up. These are:

• Body Weight – measured in either lbs or kg;
• Body fat – measured in percentage, if not known, can be calculated with the Body Fat Percentage Calculator;
• Height – measured in ft and in or centimetres.

FFMI formula and interpretation

The Fat Free Mass Index result provides the lean body mass, the FFMI and the adjusted FFMI. The three formulas involved can be found below:

• Lean = Weight in kg x (1.0 - (Body fat %/ 100.0))
• FFMI = (Lean / 2.2) / ((Height in ft x 12.0 + in) x 0.0254)2 x 2.20462
• Adjusted FFMI = FFMI + (6.1 x (1.8 - ((Height in ft x 12.0 + in) x 0.0254)))

The FFMI in an index that accounts for the amount of muscle mass one person has, correlated to their weight and height. It helps track fat loss progress along with muscle building processes.

The following table introduces the FFMI scores and their interpretation in terms of muscle mass:

* FFMI values of 26-27 indicate a suspicion of steroid usage but can still be attainable naturally.

** FFMI values of 28 – 30 are highly unlikely to be obtained naturally.

There are other types of body weight indices, such as the Body Mass Index (BMI) but compared to those, the FFMI is more specific.

For example, it addresses one of the main criticisms of the BMI, the fact that two subjects of same weight and height, will have the same BMI although different fat/ muscle amounts.

About the original study

The study has calculated the fat-free mass index (FFMI) in a sample of 157 male athletes, from which 83 were users of anabolic-androgenic steroids and 74 were not.

The normalized FFMI values of athletes who had not used steroids extended up to a limit of 25.0. The FFMI values of athletes who had used anabolic-androgenic steroids exceeded 25.0 and in some cases, even 30.0.

The study has developed the FFMI and adjusted FFMI formulas provided above, and recommendations regarding the normal average index score for males, which is around 19. Anything above 25 was considered to be indicative of steroid usage.

Another finding of the study was that FFMI can provide means for initial screening of steroid abuse. For example, it provides basis for the gold criterion screening standard for steroid use in bodybuilders.

Original reference

Kouri EM, Pope HG Jr, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med. 1995; 5(4):223-8.

Other references

1. Schutz Y, Kyle UU, Pichard C. Fat-free mass index and fat mass index percentiles in Caucasians aged 18-98 y. Int J Obes Relat Metab Disord. 2002; 26(7):953-60.

2. Kyle UG, Schutz Y, Dupertuis YM, Pichard C. Body composition interpretation. Contributions of the fat-free mass index and the body fat mass index. Nutrition. 2003; 19(7-8):597-604.