What is the average flaccid and erect penis length and girth by age and population?
Executive summary
Large, peer‑reviewed reviews and clinical measurements converge on an average erect adult penis length of roughly 5.1–5.5 inches (about 13–14 cm) and an average erect girth (circumference) near 11.7 cm (4.6 in) [1] [2]. Flaccid measurements are smaller and variable — a commonly cited clinical mean for flaccid length is ~9.2 cm (3.6 in), but ranges and methods differ by study and by age/pubertal stage [1] [3].
1. What the best reviews say: central estimates and why they cluster
Systematic reviews and clinician‑measured studies report an average erect length in the neighborhood of 13–14 cm (≈5.1–5.5 in) and an average erect circumference around 11.66 cm (4.59 in) [1] [2]. A clinical 2015 systematic review of provider‑measured data found erect length ≈13.12 cm (5.17 in) and circumference ≈11.66 cm (4.59 in) [1]. Another pooled meta‑analysis reported erect mean ≈13.93 cm (95% CI 13.20–14.65 cm) and flaccid mean ≈8.70 cm, noting regional and methodological variation [3].
2. Age and growth: when averages reach “adult” size
Pubertal timing drives most penis growth. Multiple clinical sources say puberty generally begins between about 9–14 years and most penis growth is complete by the late teens to early 20s; many clinicians treat size as essentially set by roughly age 18–21 [4] [5]. Pediatric growth‑curve work (including stretched penile length and circumference charts) shows rapid increases during puberty and gives percentiles by age, underlining that “average” varies across developmental stages [6] [7].
3. Flaccid vs stretched vs erect — different numbers, different meanings
Studies measure flaccid, stretched (SPL), and erect states; stretched length sometimes approximates erect length but is not identical. The 2015 review reported means of flaccid 9.16 cm, stretched 13.24 cm, and erect 13.12 cm — illustrating that stretched values can be close to erect but methods and examiner technique matter [1]. Another meta‑analysis pooled flaccid ≈8.70 cm, stretched ≈12.93 cm, and erect ≈13.93 cm, showing heterogeneity by study [3].
4. Variation by population, geography and method
Measurement method drives much of the apparent difference between studies: self‑reported surveys produce larger averages than measurements taken by health professionals [1] [8]. Geographic region shows systematic variation in pooled analyses, and one meta‑analysis reported an adjusted increase of average erect length over recent decades — a 24% rise across 29 years after accounting for region and sample characteristics [9] [3]. Country‑ranking pages and compilations amplify these differences but often mix self‑report and clinician data, so their cross‑country comparisons must be viewed cautiously [10] [11].
5. Percentiles, “normal” range, and clinical thresholds
Clinical papers provide percentile data: an erect penis of ~10 cm falls near the 5th percentile in some datasets, while means cluster around 13 cm [12]. The clinical definition of micropenis — usually referenced in pediatric literature — is based on measurements several standard deviations below age norms; specific thresholds depend on the dataset and age group [13] [7].
6. Conflicting findings and possible drivers of change over time
Not all analyses agree on trends. A meta‑analysis concluded erect length increased roughly 24% over 29 years after adjustments, but that conclusion depends on included studies, measurement consistency, and population sampling [9] [3]. Other sources stress that methodological differences (self‑report vs examiner measurements), sampling bias, and changing study composition can explain apparent temporal or regional shifts [8] [1].
7. Practical takeaways and limits of the record
Available sources consistently place mean adult erect length around 5–5.5 inches and erect girth near 11.6–11.7 cm [1] [2]. Age‑specific percentiles exist in pediatric and adolescent studies and show most growth during puberty with a plateau in late teens to early 20s [6] [5]. Important limitations: studies vary in measurement technique, many country rankings mix self‑report and clinical data, and not all sources report age‑stratified means in consistent ways — therefore precise “by‑age and population” tables are not uniformly available across the referenced material [1] [10] [3].
If you want, I can extract age‑stratified percentiles from the clinically measured pediatric and adolescent studies (for example the Chongqing growth charts and the Journal of Urology cross‑sectional work) and produce a practical table of flaccid/stretched/erect means or medians by age ranges — noting methodological caveats for each data source [6] [14].