What is the average erect penis length and range by age and population?

1. Why numbers differ: measurement method and sample bias

Studies that used measurements by health professionals in clinical settings tend to report values clustered around 5.1–5.5 inches erect, while self‑reported surveys often give larger means because volunteers can overestimate or because participation is biased toward men confident in their size ^{[1] [3] [2]}. A 2015 systematic review of professionally measured data found an average erect length of about 13.12 cm (5.17 in) and circumference about 11.66 cm (4.59 in) — figures widely cited in later summaries ^{[1] [2]}.

2. Age patterns: growth during puberty, stability in adulthood

Penile length grows markedly during puberty and generally reaches adult size by the end of adolescence; many sources say most growth occurs between about 13–16 years and plateaus by 18–21 years ^{[5] [6] [7]}. After reaching adulthood, average erect length is reported as stable into early middle age, with only modest changes (and possible slight shrinkage with older age due to vascular or hormonal changes), according to medical summaries ^{[6] [4]}. Specific age-by-age nomograms exist in pediatric literature but are summarized in popular health reporting rather than reproduced in every review ^[5].

3. Reported ranges and variability across studies

Published summaries and consumer health sites commonly state adult erect ranges roughly between 4.5 and 6.0 inches, or more narrowly 5.1–5.7 inches in some compilations; these ranges reflect between-study variability and different percentile cutoffs rather than a single “true” range ^{[6] [8] [4]}. The 2015 review and similar analyses measured thousands of men and found central tendency near 5.17 in (13.12 cm) but acknowledged individual variation is substantial ^{[1] [2]}.

4. Population differences: what the evidence actually shows

Available sources emphasize methodological differences more than strong, consistent population-level differences by ethnicity or geography; many large reviews aggregate data across countries and focus on pooled averages ^{[1] [2]}. Where studies rely on self-report, cultural and sampling factors can inflate differences; professional measurements reduce some biases but most summaries do not claim large, universal differences tied purely to population group ^{[1] [3]}. In short, the reporting you see across sites reflects sampling and method differences as much as—or more than—true biological variation between populations ^{[1] [3]}.

5. Girth, flaccid length, and the limits of prediction

Girth (circumference) is also commonly reported: the 2015 professionally measured average erect circumference is about 11.66 cm (4.59 in) ^{[1] [2]}. Flaccid or stretched flaccid length is a poor predictor of erect length in many men; some small flaccid penises lengthen substantially on erection while larger flaccid penises may not lengthen proportionally ^[1]. Websites and clinical guides stress standardized measurement (pressing ruler to pubic bone, measure along top to tip) to reduce error ^[3].

6. Practical takeaways and limitations of current reporting

For readers seeking benchmarks: professionally measured, pooled-data reviews place average erect length around 5.1–5.5 inches with an average circumference near 4.6 inches; commonly cited adult ranges in consumer materials are roughly 4.5–6.0 inches, reflecting between-study spread ^{[1] [4] [8]}. Limitations: many sources synthesize the same underlying reviews, self-report studies can skew the picture, and detailed age-by-age nomograms are summarized rather than fully reproduced in the consumer pieces provided ^{[5] [6] [7]}. Available sources do not mention a definitive, universally accepted “by-age and by-population” table in the supplied reporting.

If you want, I can extract the specific numbers those sources give for particular age bands (e.g., early adolescence, mid‑teens, 18–21) or list the primary academic reviews behind the pooled averages.