Is this a genetic limit?

No calculator can prove a genetic limit. It is a structure-based estimate for natural bodybuilding context.

Why use wrist and ankle size?

They are used as rough structure proxies because they change little with training.

Does FFMI prove anything by itself?

No. FFMI depends on body-fat accuracy, height and scale weight. Use it as context, not as a standalone conclusion.

Natural Muscle Potential Calculator

Estimate natural muscular potential from height, wrist, ankle, current body weight and body-fat percentage using a Casey Butt style model and FFMI context.

Height (in)

Wrist (in)

Ankle (in)

Current weight (lb)

Body fat (%)

If body fat is off, FFMI and remaining potential will be off too.

Measure the wrist at the narrowest point below the wrist bone and the ankle at the narrowest point above the ankle bone. These structure measurements change very little with training.

Maximum lean body mass

178.5 lb

Lean mass at very lean peak condition

Peak body weight

189.9 lb

Model body weight at 6% body fat

Natural potential gap

+28.9 lb

Current LBM: 149.6 lb (84% of model ceiling)

The very low body-fat target is for comparing peak condition, not a universal or safe target.

FFMI (Fat-Free Mass Index)

Values above 25 are a reason to recheck body-fat and measurements, not a diagnosis.

21.5

normalized: 21.6

Target measurements at peak condition

Structural estimate for a muscular natural peak

Body part	Target measurement
Chest	39.8 in
Upper arm	16.5 in
Forearm	13.3 in
Neck	17.1 in
Thigh	29 in
Calf	17.6 in

Estimate natural muscle potential

English intent for this topic is usually a natural-bodybuilding ceiling estimate: height, wrist and ankle structure, current body composition, FFMI and target measurements.

F F M I = \frac{l e an b o d y ma ss}{h e i g h t ^{2}}

Lean body mass is estimated from current weight and body-fat percentage.

How to use the estimate

Treat the result as a model-based reference, not a promise or diagnosis.
Small body-fat or measurement errors can move FFMI and the remaining gap.
Use the output to frame long-term expectations together with training volume and strength progress.

Frequently Asked Questions

Sources and References

Calculations are based on the listed reference sources. Links open in a new tab.

Updated: June 2, 2026

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