What are the average erect and flaccid penis sizes by age and ethnicity?

1. What the best reviews say: central estimates and ranges

The largest, measured-data syntheses converge on an erect mean in the low-to-mid 13 cm range (about 5.1–5.5 inches) and a flaccid mean around 8.7–9.2 cm (about 3.4–3.6 inches): the 2015 review cited in BJU/BMJ gives flaccid 9.16 cm and erect 13.12 cm ^{[2] [1]}, while a 2023/2024 pooled meta-analysis reported flaccid 8.70 cm and erect 13.93 cm ^{[3] [4]}. Those reviews combine hundreds of studies and tens of thousands of men measured by researchers rather than self-report, so they are the best available population benchmarks ^{[3] [4]}.

2. Age: growth stabilizes in young adulthood, limited adult decline

Available large reviews and meta-analyses indicate penile length increases through puberty and "stabilizes by age 21," and most analyses of adult samples find little or no consistent association between age and erect length across adult age ranges ^{[6] [3]}. The 2023 pooled analysis specifically reports that age was not associated with flaccid, stretched, or erect length after adulthood in adjusted models ^{[3] [4]}. Individual clinic or regional studies can show small differences by age—particularly in erectile function and girth after older age—but the broad literature does not show major length changes across adult decades ^{[7] [8]}.

3. Ethnicity and geography: small average differences, regional patterns

Meta-analyses report variation by WHO geographic region; for example, one systematic review found the largest mean stretched and flaccid lengths in studies from the Americas and larger mean circumferences in American samples ^[5]. That review and other syntheses caution that differences by race/ethnicity tend to be modest and affected by study methods (selection, measurement technique) ^{[5] [9]}. Individual summaries (including some commercial write-ups) sometimes list slightly higher averages for particular racial or ethnic groups (e.g., claims about White/Hispanic averages around 5.7 in), but these are not uniform across peer‑reviewed meta-analyses and may rely on limited or heterogeneous data ^{[10] [9]}. In short: geography/ethnicity show measurable but generally small mean differences in pooled studies ^{[5] [3]}.

4. Why study methods matter: measurement and sampling bias

Measured (clinician-measured) studies produce different means than self-reported surveys; stretched length, flaccid, and erect measurements are not interchangeable and each has method-related biases ^{[1] [3]}. Meta-analyses emphasize using investigator-measured data and excluding self-reports or clinical populations with genital anomalies to reduce bias ^{[5] [3]}. Differences between regions can reflect measurement method mix, sample age structure, and whether erections were spontaneous or pharmacologically induced ^{[3] [4]}.

5. What’s unsettled or poorly covered in current reporting

Available sources do not present a comprehensive, reliable table that breaks average erect and flaccid length by detailed single-year age bands or by granular ethnic subgroups across the same measurement protocol; they instead report pooled adult means and region-level comparisons (not found in current reporting). Likewise, precise population-level distributions by narrow age and ethnicity categories — measured consistently and nationally representative — are not provided in these syntheses ^{[3] [5]}.

6. Practical takeaways and caveats

Use pooled means as rough benchmarks: flaccid ~8.7–9.2 cm, erect ~13.1–13.9 cm ^{[2] [3]}. Expect modest regional differences—some larger means reported in the Americas—but beware that study methods, sample selection, and the state measured (flaccid, stretched, erect) explain much of the variation ^{[5] [3]}. If an individual has medical concerns (e.g., suspected micropenis or significant erectile changes), clinical thresholds and examination by a healthcare professional are the appropriate route rather than comparisons to population averages ^[11].

Sources cited: peer-reviewed systematic reviews/meta-analyses and reporting summaries ^{[1] [5] [2] [3] [4]}, plus contextual coverage and single-sample data where noted ^{[6] [7] [10] [8] [9] [12]}.