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What is the Fat Free Mass Index?

The Fat Free Mass Index or FFMI for short, was designed as an alternative measurement to Body Mass Index (BMI) that actually accounts for muscle mass. This makes it more useful for bodybuilders and athletes, as these groups of people are often classes as overweight or obese by traditional BMI scales, despite having obviously low bodyfat levels.

Use our FFMI calculator above to quickly calculator your FFMI. You’ll need your weight, height and approximate body fat percentage.

The Fat Free Mass Index (or FFMI) is quite a popular term in the health and fitness world, especially for bodybuilders and physique athletes. The problem is that it’s actually pretty poorly understood, and often used inappropriately. This article is designed to properly explain what the Fat Free Mass Index is, how to calculate it, as well as look at its pros and cons, and discuss how it relates to steroid discussions.

How to calculate your FFMI

In metric, the formula can be found below:

Lean Body Mass (in kg) divided by Height² (in Meters)

In order to calculate your FFMI you’ll also need an accurate measurement of your bodyfat percentage. The most accurate methods include things like DEXA scans and water submersion tanks, but since these are quite expensive, you’ll likely be using electronic scanner readings and/or calliper-based testing. Since these cheaper methods can be a little variable, we recommend taking a few readings and then calculating your average.

Fat Free Mass Index Pros

  • FFMI allows you to track body composition, which is a strong indicator of overall health (Duren et al. 2008) With poor body composition linked to diabetes, high blood pressure, heart disease and depression (Koksal et al. 2017)
  • Fat Free Mass Index can be a reliable indicator for various athletic performances such as sprinting and jumping. Generally speaking, having more lean muscle mass alongside less fat mass allows for greater athletic performance.
  • FFMI can also be used as an indicator of someone’s training level. In general, the higher someone’s FFMI, the more trained they are likely to be. This allows athletes and coaches to better design training plans.

Fat Free Mass Index Cons

  • Fat Free Mass Index doesn’t always scale well for people of different heights. Put simply, fat free mass isn’t just muscle, it is also things such as bones and organs, which weigh less for short people and more for tall people. This can slightly alter FFMI readings.
  • As we mentioned earlier, the FFMI requires an accurate body fat measurement to calculate, which can make it tricky to apply for lots of people.
  • The Fat Free Mass Index also doesn’t look at or assess the distribution of fat on someone’s body. Since fat in areas such as the stomach is more strongly associated with negative health outcomes, the relative distribution of fat can be important.

FFMI and Steroids

For the past few years there’s been an idea circulating that FFMI may also potentially be useful in assessing the likelihood that someone is taking performance enhancing drugs. A 1995 study (Kouri et al.) which compared 157 male athletes, as well as data from the pre-steroid to post steroid era, found that most natural athletes and bodybuilders struggled to achieve an FFMI score of more than 25.5. So you could argue that the higher someone’s FFMI is above this number, the more likely they are to be using performance enhancing drugs. With that said, there are pretty substantial issues with this approach.

FFMI may not truly be a reliable indicator of steroid usage. The study that this was based on had a lot of flaws. One of the biggest issues is that training and nutrition knowledge has advanced considerably across almost all sports, so assessing maximum muscular potential on older data is problematic. Plus, some people have great genetics, and may very well achieve significantly higher FFMI’s naturally, and some people might have FFMI’s much lower than 25.5 but actually be using drugs.

With all of this in mind, FFMI is best considered as a sliding scale of steroid use probability – but NOT as anything conclusive.

FFMI Sliding Scale for Men

<17Very little muscle, describable as “skinny”
17-20An average male, who likely does not lift weights
20-21Males who lift weights recreationally. Noticeable muscle.
21-23Very well-built
23-25Extremely muscular
25-28Exceptionally, Competively musculature – at the upper ranges of this bracket it’s highly unlikely the person is natural.
28+FREAKISHLY muscular, Highly Competitive – With incredibly few exceptions (less than 0.001% of humans) only attainable with significant drug usage

FFMI Benchmarks for Women

<14Very little muscle
14-16Average female, who probably doesn’t lift weights
16-18Athletic woman
18-19Very well-built
19-21Extremely muscular – at the upper ranges it’s highly unlikely the person is natural
20-21+FREAKISHLY muscular – With incredibly few exceptions (less than 0.001% of humans) only attainable with significant drug usage

How to practically apply FFMI to your own training

So now that you know what FFMI is, the pros and the cons, as well as its usefulness in steroid discussions, it’s time to learn how to practically apply it in your own training.

Essentially, you can use the above scales to guestimate your proximity to maximum muscular potential. So if you’re a male lifter with an FFMI of 19, you’re very unlikely to be close to your maximum potential. On the other hand if you’re a male lifter with an FFMI of 25, chances are that you’re very close to the maximum amount of muscle that you can build naturally.

In these two situations, you could reasonably conclude that the person with the higher FFMI needs to train harder and more regularly than the person with the lower FFMI. You could also reasonably conclude that the person with the higher FFMI would need to pay much greater attention to detail on their nutrition and eating plan.

However, before we get carried away, you need to remember that FFMI is only a guestimate of your potential.

You might have great bodybuilding genetics and be able to get to an FFMI of 26 or more naturally. Or you might have not so great bodybuilding genetics and struggle to get an FFMI beyond 23 despite years of consistently high quality training and nutrition.

So by all means use the scales above to guestimate proximity to your maximum potential, but use them cautiously, and make sure to measure progress lots of ways, including strength gains and measurements.

Last but not least, remember that a number doesn’t define you. FFMI can be a useful tool, but that’s all it is. It doesn’t tell you how good of a person you are, how smart you are or how good of a parent/friend/family member you are. Keep things in perspective, work hard and be the best that YOU can be.


Duren, D. L., Sherwood, R. J., Czerwinski, S. A., Lee, M., Choh, A. C., Siervogel, R. M., & Cameron Chumlea, W. (2008). Body composition methods: comparisons and interpretation. Journal of diabetes science and technology, 2(6), 1139–1146.

Koksal, U. I., Erturk, Z., Koksal, A. R., Ozsenel, E. B., & Kaptanogullari, O. H. (2017). What is the Importance of Body Composition in Obesity-related Depression?The Eurasian journal of medicine, 49(2), 102–106.

Kouri Elena M. Ph.D.; Pope, Harrison G. Jr. M.D.; Katz, David L. M.D., J.D.; Oliva, Paul B.A., (1995) Fat-Free Mass Index in Users and Nonusers of Anabolic-Androgenic Steroids. Clinical Journal of Sport Medicine: October 1995 - p 223-228.