What are the average erect and flaccid penis lengths reported in peer-reviewed studies?

1. What the peer‑reviewed literature actually reports

A high‑quality systematic review and meta‑analysis of clinician‑measured data found mean erect length ≈13.12 cm (5.16 in) and mean flaccid, pendulous length ≈9.16 cm (3.61 in); the same review reported stretched and other measures clustering near the erect value, reflecting standardized pubic‑bone‑to‑glans measurement techniques ^{[1] [2]}. More recent meta‑analyses that pooled studies by WHO region reached broadly similar ranges but note heterogeneity across datasets ^[3].

2. Why measurement method matters — clinician vs self‑report

Studies relying on self‑measurement or internet surveys consistently report larger averages than clinician‑measured studies; men tend to overestimate their size, producing upward bias in self‑reported datasets ^{[1] [4]}. Meta‑analysts therefore prefer clinician measurements that push the consensus toward the lower, more consistent estimates around 13 cm erect ^{[1] [2]}.

3. Which numbers are most quoted and why

The 2015 systematic review (and later press coverage) became a reference point because it pooled a large sample measured by health professionals and used a standardized method (pubic‑bone to tip), reporting erect ≈13.12 cm and flaccid ≈9.16 cm; many summaries and later datasets (e.g., world rankings or 2024–25 meta‑analyses) use that as their baseline ^{[1] [2] [4]}.

4. Variation, biases and statistical caveats

Measured averages vary by study sample size, participant age and geography; publication bias (studies with striking or significant results being more likely published) and differences in how “flaccid,” “stretched,” and “erect” are operationalized can shift pooled estimates ^[3]. The 2024 systematic review explicitly warns that age demographics and publication bias could confound comparisons and possibly overestimate averages in published literature ^[3].

5. Regional and temporal claims — competing findings

Some recent papers and commentators have suggested increases over time (for example, claims of a 24% rise in average erect length across decades), but such claims depend heavily on which studies are pooled, whether self‑reports were included, and adjustments for sampling differences; pooled clinician‑measured meta‑analyses remain a more conservative reference ^{[5] [3]}. Regional rankings (country lists) often mix study types and adjusted self‑reports, producing larger cross‑country differences than clinician‑measured research supports ^{[4] [6]}.

6. What remains uncertain or unaddressed in available reporting

Available sources discuss heterogeneity, measurement bias and some temporal trends, but they do not settle causation for any apparent changes (e.g., whether true population changes exist or reflect changing study methods) — “why” size may differ over time or place is not resolved in the cited analyses ^{[3] [5]}. Specific factors such as longitudinal individual‑level changes, genetic vs environmental contributions, or comprehensive global sampling with uniform methods are not fully described in the current reporting ^[3].

7. Practical takeaway for readers

If you want the closest peer‑reviewed, clinician‑measured consensus: use ≈13.1 cm (5.16 in) erect and ≈9.16 cm (3.61 in) flaccid as working averages, while noting that credible studies show variation and that self‑reports skew higher ^{[1] [2]}. For comparisons across countries or time, scrutinize whether data are clinician‑measured or self‑reported and whether analysts adjusted for sample and methodological differences ^{[3] [4]}.

Sources: Systematic reviews and meta‑analyses and mainstream summaries reporting clinician‑measured averages (see Veale et al. and related meta‑analyses summarized in the literature) ^{[1] [2] [3]}.