About

For natural lifters, the question "How big can I get?" is fundamental. While training and nutrition are variables you control, your bone structure dictates the physiological ceiling for muscle tissue accretion. This tool employs Casey Butt's Formula, a highly regarded predictive model derived from the analysis of champion natural bodybuilders from the pre-steroid era (1930s-1950s).

By analyzing the correlation between skeletal frame size (wrist and ankle circumference) and height, the model estimates the maximum lean body mass (LBM) a drug-free individual can realistically achieve at a given body fat percentage.

Formulas

The Casey Butt equation for Maximum Lean Body Mass (LBM) is:

LBM = H^1.5 × (√W22.6670 + √A17.0104) × (%bf224 + 1)

Where:

H = Height in inches
W = Wrist circumference in inches (styloid process)
A = Ankle circumference in inches (smallest point)
%bf = Target body fat percentage

Reference Data

Measurement	Why it matters?	Typical Range (Male)
Wrist Circumference	Proxy for upper body bone thickness.	6.5″ - 8.0″
Ankle Circumference	Proxy for lower body bone thickness.	8.0″ - 10.0″
Height	Determines overall frame length.	Variable
Target Body Fat	Required to normalize LBM calculations.	8% - 12% (Stage Ready)

Frequently Asked Questions

This formula predicts the maximum *natural* lean mass for a lean individual (approx 8-10% body fat). It is a statistical ceiling based on elite genetics. While 99% of the population will not exceed this, outliers exist, though usually by small margins without pharmaceutical assistance.

Wrist: Measure below the wrist bone (styloid process) on the hand side. Ankle: Measure at the smallest point above the ankle bone. The tape should be tight but not compressing the skin.

There is a strong physiological correlation between the cross-sectional area of bone and the muscle belly it can support. A larger frame (skeleton) provides a larger surface area for muscle attachment and hormonal support for greater tissue mass.