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FFMI Calculator

FFMI is a measurement of how much muscle you have per unit of height. Although imperfect, research shows FFMI is a reliable indicator of whether or not someone is taking or has taken steroids to build muscle. You can calculate your FFMI by dividing your fat-free mass (your total body weight minus the weight of your body that’s fat) in kilograms by your height in meters squared, or simply entering your height, weight, and body fat percentage into the Legion FFMI Calculator.

Frequently Asked Questions

What’s the difference between FFMI and normalized FFMI?

FFMI is simply how much muscle you’re carrying per unit of height. The problem with only using FFMI, though, is that as height increases, so does FFMI, regardless of whether or not someone has taken or is taking steroids.

Normalized FFMI takes this into account by normalizing people’s FFMI to the average height of the participants in the group being measured. In the largest and most commonly cited study on this topic, the average height of the participants was 5’11, so this is generally the height used when computing normalized FFMI (it’s also fairly close to the average height of American men—5’10).

If this all seems confusing, don’t worry—the key thing to remember is that normalized FFMI is slightly more accurate when comparing the FFMIs of different people, especially when they’re significantly taller or shorter than average.

I’ve heard FFMI is bogus. Is there any scientific evidence behind this method?

Yes, quite a bit actually.

In the most famous and comprehensive study on FFMI and steroids, scientists at McLean Hospital calculated the FFMI of 157 young male athletes from around the Los Angeles and Boston area, including several elite bodybuilders and world-record holding strongmen, as well as some gents undergoing a testosterone injection study.

Of these guys, 31 admitted to taking steroids in the past, 52 admitted to taking steroids within the previous year, and 74 claimed they had never taken steroids. The researchers also had everyone take a urine test to at least attempt to partially validate their claims. After analyzing the data, the scientists found the steroid users had an average FFMI of 24.8 while the purported non-users averaged at 21.8.

Another significant finding was that not a single natural participant had an FFMI over 25, whereas many “enhanced” ones did.

This and other research shows that if someone has a normalized FFMI of more than 25, there’s an extremely good chance they’re taking or have taken steroids.

If someone has an FFMI of less than 25, does that mean they aren’t on steroids?

Not necessarily.

Most steroid users don’t look like professional bodybuilders or physique athletes (almost all of whom are sporting FFMIs north of 25). In fact, many look far more “normal” than you might think.

Some have sub-par genetics, some take smaller doses, some don’t train intensely or frequently enough, some don’t eat well or sleep enough, some don’t want to be that big, and some (“influencers,” usually) even stage-manage their FFMIs by lying about their height, weight, and body fat percentage to avoid being pegged as drug users.

For example, you could maintain a very “aesthetic” physique lifting weights just once or twice per week for 30 to 45 minutes, eating fast food every day, and paying no attention to your calories and macros . . . if you also take steroids. Steroids even allow you to build muscle, stay lean, and eat quite a bit of food without going to the gym, which is why some sedentary people take them, too.

Finally, having used steroids in the past can make it easier to get and stay unusually muscular and strong when “clean.” Steroid use alters your muscles at the cellular level in a way that makes it permanently easier to gain and maintain unnaturally large amounts of muscle. In other words, every pound of muscle you gain while on steroids contributes to your overall muscularity for the rest of your life.

There are plenty of guys and gals who tell people they’re “natural” because they’re not currently on drugs, while neglecting to mention they took steroids in the past. In many cases, people with suspiciously high normalized FFMIs (24+) used steroids to permanently prop up their FFMI, even though they don’t take them anymore.

At bottom, then, here’s what the evidence says about determining whether someone is natty or not:

  • If someone’s FFMI is over 25, it’s almost certain they’re taking or have taken steroids.
  • If someone’s FFMI is between 24 and 25, then it’s likely they’re taking or have taken steroids.
  • If someone’s FFMI is between 22 to 23, they maintain a fairly normal body fat percentage (they aren’t “shredded” year round), and they’ve been training consistently for 3+ years, they’re probably natural.
  • If someone’s FFMI is between 21 to 22, they’re also probably natural.
  • If someone’s FFMI is between 18 to 21, they likely don’t even lift so who cares. 🙂

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