The FFMI (fat free mass index) formula estimates the amount of muscle mass that you can carry after maximizing your physique with +10 years of natural bodybuilding training.

In the formula, your muscular potential is determined based on the circumference of your wrists and ankles.

The logic behind this is great because the wrists and ankle measurements show the thickness of your bones and the thickness of your bones determines how  much muscle mass your body can support.

In general, people with thicker bones naturally carry more muscle mass and they’re also able to build more.

This is why you will see that individuals with very thick wrists, ankles and necks and wide rib cages also tend to have above average levels of muscle mass.

According to Holway in The Sports Gene (2013, p. 125) each kilogram (2.2 pounds) of bone supports a maximum of five kilograms (11 pounds) of muscle.

Here’s a quote taken from The Sports Gene, p. 125:

Most olympic athletes whom Holway has measured, like discus throwers and shotputters, have skeletons that are only about 6.5 pounds heavier than those of average men, but that translates to more than 30 pounds of extra muscle that they can carry with proper training.

As a result the FFMI formula is the best thing natural bodybuilders and physique athletes have to estimate our natural muscular potential.

My Results With The FFMI Formula After 10 Years of Training

I inputted my measurements into the FFMI formula calculator:

• Body-fat percentage: 18%
• Height: 188 CM
• Weight: 103 KG
• Wrist circumference: 18 CM
• Ankle circumference: 24 CM
• Torso circumference: 126 CM
• Upper arm circumference: 44 CM
• Forearm circumference: 34 CM
• Neck circumference: 39 CM
• Thigh circumference: 74 CM
• Calf circumference: 43 CM

Here are the results I got:

My FFMI: 23.4

Muscle Size By Body-Part:

And here’s how that looks in terms of bodybuilding progress for me:

How I looked after around 7-12 months of progressive barbell training, age 18, skinny-fat and just diagnosed with hypogonadism:

And here’s after around 10 years of training, mostly with bodyweight:

The FFMI Formula Is Incredibly Accurate

My result with the formula was a FFMI of 23.8 which puts me in the category between “internationally competitive bodybuilder” and “average steroid user”.

This may sound impressive but I believe that my FFMI measurement is a bit inflated due to being at an above average body-fat level.

First and foremost, when it comes to body-fat level, there’s no 100% accurate method to determine it.

The most accurate scanning method of estimating body-fat is a DEXA scan but even that method is off by +/- 3% which means that if it says you are 15% you could be anywhere from 12-18%. That’s a fairly wide range.

The second method commonly used is body-fat scales. These are all highly inaccurate.

Then you have the caliper skin-fold test. This method can be quite accurate if you have someone experienced doing it.

The final method is to look at guideline photos online, like the one below:

Looking at body-fat guideline photos is the most accessible and practical method to estimate your body-fat percentage. (This doesn’t mean it’s the best way to track fat loss progress. I personally use a combination of waist and hip measurements and photos to track clients’ fat loss progress.)

Based on these photos I estimated my own body-fat to be somewhere around 18%.

This is a problem because you will be able to carry more muscle mass at a higher body-fat level.

There’s no way that I can maintain my current muscle mass if I lean out to 12% body-fat.

How do I know?

Because from 2013-2017 I stayed at a relatively low body-fat level:

I had to train hard for 2 hours 5-6 days per week to maintain the level of leanness I had.

Back then, my shoulder, chest and arm measurements were slightly smaller than now:

• Shoulders: 145 CM vs 140 CM.
• Torso: 127 CM vs 124 CM.
• Arms: 44 CM vs 42.5 CM.

Also, my weight was around 94 KG instead of 103 KG.

The FFMI formula works best when used for individuals at 4-12% body-fat, therefore I’ll input my old measurements into the formula.

Here are the results:

When I input my old measurements into the formula, I get an FFMI of 22.9 which is a bit lower than the 23.8 I got at higher body-fat.

The predictions of the formula are also highly accurate for all measurements except my torso which exceeded the formula with 5% and thigh size which I exceeded with 8%.

In contrast, the calves and neck are 2 body-parts that are a few CM behind the maximum. These are 2 naturally small body-parts for me and I haven’t put much effort into training them. If I trained them hard and consistently for 1-2 years I believe they would fit perfectly with the formula too.

Conclusion

The FFMI formula is the most accurate tool you have as a fitness athlete / bodybuilder to estimate what your body can look like after 5-10 years of hard and consistent training.

A lot of people will tell you that the peak measurements are only achievable by a select few people with amazing genetics.

I used to believe that too early in my training when I first came across the formula.

I was diagnosed with hypogonadism around age 18 and after 2 years of training I looked exactly the same as when I started:

I can tell you that after being diagnosed with hypogonadism and seeing 0 visible progress in 2 years of hard training, I also thought that it’s impossible for me to get anywhere near the peak measurements in the FFMI formula.

However, I eventually found out that my body only responds to all out full body training 5-6 days per week, primarily with bodyweight exercises and secondarily with dumbbell, machine and cable isolation work. It was the complete opposite approach of what I had thought for years was ideal (heavy barbell training 3 days per week).

A constant sustained stimulus was the key to make my body grow and I combined that with a much better diet and lifestyle to also boost my testosterone levels 270%.

Over time, I maxed out my physique and got content with the muscle I built.

In total, it took me around 7 years to reach my peak measurements at low body-fat levels (12% body-fat or so which requires a lot of effort for me to maintain) and out of that 5 years were truly intelligent training that I responded to.

Therefore, to be on the safe side, give yourself 10 years and experiment with different approaches.

In addition to that, remember that genetically gifted individuals can even reach an FFMI of over 25 which is higher than the average steroid user.

I’m not in that group of people, but who knows, maybe you are? There’s only one way to find out and that is to train hard for a long time, experiment with different approaches and see where it takes you.

Be proud but stay hungry!

Oskar Faarkrog, ISSA Certified Personal Trainer