Clinical Accuracy Verified
Data verified on 2026-04-20 Reviewed by Michael R. Chen, CPA, CFP®
🧬
Natural Muscular Potential
Predict your maximum drug-free muscle size (FFMI) based on your wrist and ankle bone structure.
in
Example: 5'10" is 70 inches.
in
Measure the smallest part of your wrist, below the bone.
in
Measure the smallest part of your ankle, above the bone.
%
🧬 Genetic Limit Prediction
Max Lean Body Mass180 lbs
Total Weight @ 10% BF200 lbs
FFMI Score25.8
Maximum Measurements
Chest
48.3"
Biceps
18"
Thighs
42.4"
Calves
29.1"
⚠️ An FFMI over 25 is generally considered the upper limit for natural bodybuilders. You have elite genetics!
Casey Butt's Model
Developed by analyzing elite drug-free bodybuilders (pre-steroid era). It uses bone structure to determine the maximum amount of muscle a frame can support.FFMI (Fat Free Mass Index)
- 19-20: Average Male
- 21-22: Well Trained
- 25: Genetic Ceiling (Natural)
- >26: Highly likely to be enhanced
Results Natural Muscular Potential
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