Maximum Muscular Potential Calculator
Enter your height, wrist, ankle size and target body fat to see your genetic potential estimate.
Result
How it is calculated
All three lengths are in centimetres and are converted to inches (÷ 2.54). Lean mass in pounds is then FFM = height × (0.20 × wrist + 0.12 × ankle), with every length in inches. The target body fat percentage turns that lean mass into a total body weight: max weight = FFM ÷ (1 − target body fat % ÷ 100). Results are shown in kilograms (pounds × 0.45359237) and in pounds, to one decimal. Inputs outside human limits show no result: height must be 50 to 272 cm, wrist 5 to 40 cm, ankle 10 to 50 cm, and target body fat above 0 and below 100. The formula is a simplified rule of thumb that rewards a bigger frame; it ignores age, training history and sex, and the number is a ceiling estimate for a natural lifter, not a goal that everyone reaches.
Worked example
A person 180 cm tall with an 18 cm wrist, a 23 cm ankle and a 10% target body fat. In inches: height 70.87, wrist 7.09, ankle 9.06. FFM = 70.87 × (0.20 × 7.09 + 0.12 × 9.06) = 70.87 × 2.504 = 177.4 lb, which is 80.5 kg. Max weight = 177.4 ÷ (1 − 0.10) = 197.2 lb = 89.4 kg.
Common mistakes
- Measuring wrist or ankle at the widest, fleshy spot rather than just above the bone, which inflates the frame and the answer.
- Entering the target body fat as a fraction (0.10); the field takes a percentage like 10, and 0.10 would mean a 0.1% target.
- Typing inches instead of centimetres. A 7-inch wrist entered as 7 gives a tiny frame and a far too low weight.
- Treating the result as a promise: it is a modelled ceiling and says nothing about how many years of training are needed to reach it.
- Entering a very low target such as 3–4% and then reading the weight as healthy or sustainable; the formula only divides by the leanness you ask for.
About this calculator
Formulas for natural maximum muscular potential — popularized by researcher Casey Butt's regression model and echoed in Martin Berkhan's simplified version — estimate the largest lean body weight a natural (non-steroid-using) athlete can realistically build at a given body fat percentage, using height along with wrist and ankle circumference as proxies for skeletal frame size. The underlying premise is that muscle mass is bounded by joint and bone structure — someone with a larger frame (thicker wrists and ankles relative to height) has more room to add muscle than someone with a smaller frame, regardless of training.
Bodybuilders, strength coaches, and drug-testing federations reference these genetic-potential formulas both as realistic long-term goal-setting tools for natural lifters and, more controversially, as a rough screening heuristic for identifying physiques that may exceed what's achievable naturally, since Butt's model was built from data on drug-tested elite natural bodybuilders.
This calculator takes your height, wrist and ankle circumference, and target body fat percentage to estimate your natural maximum muscular body weight potential. It uses a simplified formula rather than Casey Butt's full regression: lean mass is your height multiplied by 0.20 times wrist plus 0.12 times ankle (all in inches), then divided by one minus your target body fat to give a body weight. Treat it as a rough ceiling, not a precise prediction.
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