What is the average erect and flaccid penis length in the United States by age group?

1. What the major summaries say — a narrow consensus on adult erect length

Multiple medical and health-review outlets cite a consistent central estimate for adult erect length: about 5.1 to 5.5 inches (12.9–13.97 cm) as the most defensible average based on pooled studies and reviews; Medical News Today and other summaries repeat that range as the best current scientific consensus ^{[1] [7]}. Wikipedia’s compilation of measurement studies likewise notes that clinically measured studies tend to give averages near that same band, and that self-reported surveys often inflate numbers ^[5].

2. Flaccid length and “stretched” length — different measures, different meanings

Reporting emphasizes that flaccid, stretched, and erect measurements are distinct and not interchangeable: a “stretched” length sometimes correlates with erect length but not perfectly, and studies show considerable variation in flaccid measures depending on temperature, technique and observer ^[5]. Health sites commonly cite mean flaccid values near roughly 3.5–4.0 inches (about 9–10 cm) for adults, but those values vary across studies and measurement methods ^{[3] [4]}.

3. Growth timeline — when most change happens

Sources agree that most penile growth occurs during puberty and stabilizes by late adolescence or early adulthood, commonly around age 21; one review says length and girth tend to stabilize by 21 ^{[2] [6]}. Pediatric-focused guides list approximate flaccid size ranges through childhood and adolescence but emphasize broad individual variation and that published adolescent data differ by study ^[4].

4. Limits of available data — no detailed U.S. age-group table in these sources

None of the provided sources presents a comprehensive, peer-reviewed U.S.-specific table that gives average erect and flaccid length for narrow age brackets (e.g., 10–12, 13–15, 16–18, 19–21, 22–30, etc.). The Parents.com summary cites age-related ranges based on clinical teaching and older references but acknowledges that published data on adolescents and adults vary by source; Wikipedia and medical reviews compile worldwide study results rather than a U.S.-only, age-stratified dataset ^{[4] [5] [1]}.

5. Measurement biases and why numbers vary

Experts cited in the sources warn that method matters: self-measured and self-reported surveys typically yield larger averages than clinician-measured studies because of volunteer and reporting biases ^[5]. Temperature, measurement protocol (flaccid vs stretched vs erect), and participant selection (clinical vs online volunteers) produce systematic differences between studies ^{[5] [1]}.

6. Practical takeaways and clinical definitions

Clinically, “micropenis” is defined by a statistical cutoff (about 2.5 standard deviations below the mean for age), and precise assessment matters for medical decisions; for most people, penis size stabilizes after puberty and falls near the adult average band cited above ^{[4] [2]}. Medical reviews also highlight that perceptions of “normal” often exceed measured averages, which can drive unnecessary cosmetic procedures ^[1].

7. If you need age-specific numbers — what to do next

Because the supplied reporting lacks a validated, U.S.-only, age-by-age table, the responsible next steps are: consult peer-reviewed pediatric growth studies or systematic reviews that explicitly publish age-stratified penile measurements; ask a pediatric urologist or endocrinologist for clinical growth charts; or request the specific datasets cited in meta-analyses underlying the 5.1–5.5 inch adult average (noted in public reviews) to see age breakdowns if they exist ^{[1] [5] [4]}.

Limitations: The above synthesizes only the provided sources; they agree on a general adult erect average (5.1–5.5 inches) and on puberty-driven growth stabilizing by about age 21, but they do not supply a comprehensive U.S. age-group table broken out by flaccid and erect averages ^{[1] [2] [3]}.