Fit Phase

Calculator

Maximum muscular potential

Based on Casey Butt's model for drug-free lifters. Your wrist and ankle are proxies for your frame — bones you can't train — so they anchor a realistic ceiling for lean mass and each measurement at a lean condition.

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in
in
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Your ceiling

—lbs
Maximum lean body mass
Maximum weight at that body fat — lbs
Frame ceiling (body-fat independent) — lbs
Chest— in
Biceps (each)— in
Forearms (each)— in
Neck— in
Thighs (each)— in
Calves (each)— in
A ceiling is not a forecast. It's the upper bound for your frame at a very lean, well-developed condition — most lifters never need it, and getting close takes years of consistent training and nutrition. Fit Phase is built for that consistency: it plans your phases and calibrates your targets from your own data. Join the waitlist →

Uses Casey Butt's published equations from Your Muscular Potential, including the body-fat term in the lean-mass prediction (measured lean mass rises somewhat with body fat). The frame ceiling row is the body-fat independent part of the model — the number to use as a hard lean-mass cap. Body fat is accepted between 3% and 20%, the range the model was built on. Measurement predictions assume a lean, well-developed condition; wrist and ankle are measured at the narrowest point. Educational estimate, not a guarantee or medical advice.