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Your Maximum Natural Muscle Mass potential.

Estimate your drug-free muscle ceiling using three evidence-based models — Casey Butt, Martin Berkhan (Leangains) and Alan Aragon — based on your height and skeletal frame size.

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Genetic Potential — Maximum Natural Muscle Mass
Butt, Berkhan & Aragon models — your natural drug-free ceiling
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Your data

in
in
in
lb
🏆

Your potential

— lb LBM
Casey Butt model
Butt
—
lb LBM
Berkhan
—
lb LBM
Aragon
—
lb LBM
⚠️ These models were developed from male bodybuilder data. For women, estimates may overstate potential by 20–30%. Use as a relative reference only.
Max bodyweight at ~10% BF (Butt model, competition lean)—
Max bodyweight at ~5–6% BF (stage lean)—
FFMI at max LBM fat-free mass index—
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How it's calculated

Three models, one number: your natural ceiling

The Genetic Potential calculator estimates your maximum drug-free lean body mass (LBM) using three models. The Casey Butt formula uses height, wrist and ankle circumference; the Martin Berkhan (Leangains) model uses height; and the Alan Aragon model uses height. For a 5'9" (175 cm) man with a 7" wrist and 8.5" ankle, the models predict a maximum LBM of approximately 185–195 lb at peak condition.

Your skeletal frame — indicated by wrist and ankle circumference — limits how much muscle tissue your body can structurally support. Taller people with larger joints can typically build more total muscle mass. These models were validated against elite natural (drug-free) bodybuilders competing at their peak condition.

Casey Butt: LBM = H1.5 × (√W/22.667 + √A/17.011) × (H/4.5 × BF/100 + 1)
Berkhan (Leangains): LBMpeak = H(cm) − 100 (at ~5–6% BF)
Aragon: Max BW(lb) = H(in) × 2.0 (at ~10% BF for intermediate/advanced lifters)
  1. 1
    Convert inputs to inches / centimetres as needed
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  2. 2
    Casey Butt: combine height, wrist and ankle into LBM estimate at 5% BF
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  3. 3
    Berkhan: height (cm) − 100 = max LBM in kg at stage lean
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  4. 4
    Aragon: height × 2.0 → max bodyweight at ~10% BF; derive LBM
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Understand the terms

Lean Body Mass (LBM)
Total body weight minus fat mass. Includes muscle, bone, organs, connective tissue and water. The key metric used by all three genetic potential models.
Natural potential
The estimated upper limit of muscle mass achievable without the use of anabolic-androgenic steroids or other performance-enhancing drugs. Differs per individual based on genetics, frame size and training consistency.
Frame size
An indicator of skeletal structure, approximated by wrist and ankle circumferences. Larger-framed individuals can typically support more muscle mass.
Fat-Free Mass Index (FFMI)
LBM (kg) divided by height² (m²). A normalised measure of muscularity. Values above 25 are rarely seen in drug-free athletes; 22–24 is typical for advanced natural lifters.
See the full glossary →
Disclaimer: estimation tool for informational and planning purposes. The Butt, Berkhan and Aragon models were developed from analysis of elite male drug-free bodybuilders. Individual results may differ based on genetics, training quality, nutrition and measurement accuracy. Results for women may overstate potential. Does not replace assessment by a qualified coach, sports scientist or physician.
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Frequently asked questions — Genetic Potential

How much muscle can I gain naturally?
Natural muscle gain varies widely by genetics, frame size, age and training history. Most men can add 20–40 lb of lean mass over a lifetime of training. Year 1 typically yields 10–25 lb, year 2 around 5–10 lb, and gains slow considerably after year 4. The Casey Butt, Berkhan and Aragon models give you a research-grounded upper bound based on your frame.
How accurate are genetic potential models?
These models were derived from measurements of elite natural bodybuilders competing at their peak. They represent what is achievable with optimal training, nutrition and genetics — not an average expectation. Most natural lifters reach 80–90% of the theoretical ceiling. Expect a margin of ±5–10% around model outputs.
What is the Casey Butt formula?
Casey Butt analysed the measurements of hundreds of drug-free bodybuilders to derive a formula that predicts maximum lean body mass from height, wrist circumference and ankle circumference. These skeletal measurements correlate with muscle insertion points and the total cross-sectional area muscles can grow to. The formula: LBM = H^1.5 × (√W/22.667 + √A/17.011) × (H/4.5 × BF/100 + 1) where H = height in inches, W = wrist in inches, A = ankle in inches, BF = body fat % at peak.
How long does it take to reach genetic potential?
Most research and coaches estimate 8–12 years of consistent, progressive resistance training with adequate protein and sleep. The trajectory is front-loaded: the first 1–2 years bring the largest gains ("newbie gains"), while the last 10–20% of potential may take years to approach. Most lifters never fully reach their theoretical ceiling.
Does height affect muscle potential?
Yes. Taller individuals generally have longer muscle bellies with greater potential cross-sectional area, giving them a higher absolute LBM ceiling. However, shorter individuals often appear more muscular at the same LBM because mass is distributed over a shorter frame. All three models (Butt, Berkhan, Aragon) incorporate height, with Berkhan's formula being entirely height-dependent.

📚 Learn more — official sources

🔬 Study Kouri et al. (1995) — FFMI in natural vs. steroid-using bodybuilders Classic study showing that natural bodybuilders rarely exceed an FFMI of 25, providing an independent upper bound consistent with the Butt and Berkhan models. See on PubMed → 🔬 Study Haun et al. (2019) — Skeletal muscle hypertrophy rates in resistance training Review of hypertrophy literature quantifying typical muscle growth rates over the first years of training, supporting the diminishing-returns trajectory of natural potential models. See on PubMed → 🏛️ Organization NSCA — Muscle hypertrophy: mechanisms and training variables National Strength and Conditioning Association overview of the physiological mechanisms driving muscle hypertrophy and how training variables affect natural gains. See official source → 🔬 Study Morton et al. (2018) — A systematic review of protein supplementation for muscle gains Meta-analysis on how dietary protein affects lean mass gains in resistance-trained individuals, relevant to approaching genetic potential ceilings. See on PubMed →

About the Genetic Potential Calculator

The Genetic Potential Calculator estimates the maximum lean body mass a natural (drug-free) athlete can achieve, using three independently developed models. The Casey Butt formula is the most anatomically grounded — it incorporates wrist and ankle circumferences as proxies for bone and tendon size, which limit how much contractile tissue a skeleton can support. The Berkhan (Leangains) model offers a simple height-based estimate calibrated to stage-lean competition weight. The Aragon model predicts maximum bodyweight at ~10% body fat from height, widely used by coaches for target-setting.

Together, these three models give you a range rather than a single number, which is more useful for realistic goal-setting. If your current lean body mass is well below all three models, you have meaningful growth potential ahead. If you are already approaching the lower of the three estimates, you are likely an advanced natural lifter. Use this tool alongside the FFMI calculator and body fat tools to track your progress relative to your individual ceiling.

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