This Fat free mass index FFMI calculator computes the muscle mass index for bodybuilders and fitness enthusiasts based on weight, body fat and height. Read more about the formulas used and discover what the score indicates about natural or steroid muscle mass build up.

Unit system:*
Body fat:*

How does this Fat free mass index (FFMI) calculator work?

This is a health tool that is able to assess your body mass while also taking into account muscle and fat mass. There are three factors that are being used in the calculations and these are the weight, body fat percentage and height. The tool is flexible so you can use either the English or the Metric measurement units and as well you can make as many calculations as you’d like.

The results provided by this fat free mass index calculator include the lean body mass, the FFMI and the adjusted FFMI. Each of the three formulas used is explained below. One of the first steps in the calculation is to deduce lean over gross body mass with the following equation:

■ 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)))

What is FFMI and what does it show?

First of all we should start by mentioning that this is an index used to account for the amount of muscle mass one person carries in correlation to their weight and height. It belongs to the class of body weight indexes along with the BMI but it takes things to a different level and becomes much more specific.

It also addresses one of the criticisms of BMIs which is that two persons with different weights and heights can have the same BMI but different fat/ muscle amounts. BMI can class a person with a lot of muscular mass under a higher class, maybe a negative health indication regardless of body type because it doesn’t consider the difference of tissues and only uses the overall weight.

In trying to address these problems, studies have been made, as cited in the references section, on steroid and non steroid users, bodybuilders in contest shape, to determine an index and its range, something that could adapt to specific body masses.

Besides the formula of FFMI and adjusted FFMI it was concluded that a normal average index score for males is around 19 while everything going above 25 is indicative of steroid usage.

This also marked the beginning of a gold criterion screening standard for steroid use in bodybuilders. However, this doesn’t necessarily mean that a person cannot attain naturally a score of 30 but it is highly unlikely.

Basically this index helps track fat loss progress as well as muscle building processes you might be going through and is often used by athletes, fitness enthusiasts or body builders.

FFMI interpretation and norms for men

As discussed above, the proposed studies have reached the following conclusions in regard to what the scores mean about the body condition of the subjects. These scores are now used in practice and provide useful guidelines to everyone who wants to know where they stand in terms of muscle mass:

■ 16 – 17: below average

■ 18 – 19: average

■ 20 - 21: above average

■ 22: excellent

■ 23 – 25: superior

■ 26 – 27: scores considered suspicious but still attainable naturally

■ 28 – 30: highly unlikely scores to be obtained naturally without steroid usage

Example calculation of fat free mass index

Let’s take for example a fitness enthusiast with a weight of 180 lbs, 12% body fat and 5 ft 10 in height. The result from the above form will be

- Lean mass = 71.85 kg / 158.40 lbs

- FFMI = 22.78

- Adjusted FFMI = 22.91

When trying to make all sorts of calculations and you want to discover how much muscle mass you can build at your stature you can try different numbers in the weight and body fat fields and see which combination will take you to a value close to 25, which is considered an obtainable FFMI score without any chemical intervention.

Therefore this calculation can provide useful information about the muscle mass and even establish whether it is possible to have been obtained in a natural way or not, but the BMI for men can still be a tool to check whenever the health status of the weight needs to be assessed at a glance.


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

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

11 Aug, 2015