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Maximum muscle potential calculator

How much muscle you can build without drugs: your fat-free mass index and three published estimates of the ceiling.

Sex
From a body fat scale, calipers or a DEXA scan.
Optional. The smallest point, between the hand and the wrist bone.
Optional. The smallest point, just above the ankle bones.
The leanness the maximum weight is given at.

Fill in the fields to see your result.

How it is calculated

FFMI (fat-free mass index) is lean mass in kg divided by height in metres squared, plus 6.1 × (1.8 − height) so that tall and short people compare fairly. In a 1995 study of strength athletes, Kouri and colleagues found that men who had never used steroids reached at most about 25. For a man of 1.80 m that is 81 kg of lean mass.

Martin Berkhan’s rule of thumb: in stage condition, at about 5 % body fat, a drug-free man’s top weight in kg is his height in cm minus 100. The calculator counts 95 % of it as lean mass.

Casey Butt’s formula, built from drug-free bodybuilding champions, adds your frame: maximum lean mass (lb) = H^1.5 × (√W ÷ 22.667 + √A ÷ 17.0104) × (1 + BF ÷ 224), with height H, wrist W and ankle A in inches and BF the body fat %. The calculator converts from and to cm and kg.

These are averages from exceptional athletes, not a promise. Most people who train well for years end up a few kilograms below them, and a body fat reading can be off by several percent.

Questions

How much muscle can you build naturally?

Drug-free men rarely go past a fat-free mass index of about 25. For a man of 1.80 m that is about 81 kg of lean mass, or about 90 kg at 10 % body fat.

What is FFMI?

The fat-free mass index is lean body mass in kg divided by height in metres squared. The normalised version adds 6.1 × (1.8 − height in m) so people of different heights compare fairly.

Why do wrist and ankle size matter?

Casey Butt found that bone structure, measured at the wrist and ankle, predicted how much muscle drug-free champions carried: a larger frame holds more muscle.

How accurate are these estimates?

They describe the best drug-free athletes, so they are a ceiling, not a target. Genetics, years of training and the accuracy of your body fat reading all move the result by several kilograms.

Tviky gives general training information, not medical advice. If you are injured or in pain, see a physiotherapist before training.

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