What large-scale U.S. studies report average erect and flaccid penis length and girth?

1. What the big studies actually measured

Large syntheses focused on studies where a trained examiner measured men in clinic settings, not self-reports; that distinction matters because self-measured data tend to be larger and more variable ^[5][2]. The 2015 review summarized in BMJ and BJU International pooled data from more than 15,000 men and reported mean flaccid 9.16 cm and erect 13.12 cm ^[1]. A more recent systematic review and meta‑analysis (search through Feb 2024) pooled many studies and reported means of flaccid 9.22 cm, stretched 12.84 cm, erect 13.84 cm, flaccid circumference 9.10 cm and erect circumference 11.91 cm ^[3][4].

2. Why numbers differ between papers

Differences come from sampling, measurement method, and whether measurements were bone‑pressed (pubic fat compressed) or not. Meta‑analyses that require examiner‑measured data produce lower, more consistent averages than self‑reported studies, which often inflate means ^[5][2]. Geography and study periods matter too: the WHO‑regions meta‑analysis found larger stretched and flaccid means in “Americas” samples (stretched ~14.47 cm, flaccid ~10.98 cm in that subgroup) ^[3][6].

3. Girth (circumference): the parallel story

Girth is less often reported but the large 2024 meta‑analysis gave pooled flaccid circumference ≈9.10 cm and erect circumference ≈11.91 cm ^[3]. Earlier provider‑measured syntheses cited in summaries report erect girth around 11.66 cm (≈4.6 in) and flaccid girth near 9.31 cm ^[5][7].

4. Trends and contested claims

Some recent analyses claim increases over decades. A systematic review covering studies to 2021 reported an upward trend in average erect length from the 1990s to 2021, but trend work is sensitive to which studies are included and to measurement heterogeneity ^[8][9]. The WHO‑regions meta‑analysis and earlier reviews note heterogeneity and risk of bias across included studies, so claims of temporal change remain contested in the literature ^[4][8].

5. Limitations readers must know

All large syntheses warn of limitations: volunteer bias (men who agree to be measured may differ from general populations), inconsistent measurement protocols (bone‑pressed vs non‑bone‑pressed, base vs mid‑shaft circumference), and geographic sampling skew (many studies drawn from specific clinics or regions) ^[6][5]. The 2024/25 meta‑analysis explicitly limited inclusion to studies where a healthcare professional measured penis size but still noted moderate/low risk of bias and variable standardization across studies ^[4][3].

6. What to use if you need a single reference number

If you need a defensible clinical reference based on provider‑measured data, use the frequently cited pooled results: erect ≈13.1–13.8 cm (≈5.1–5.4 in) and flaccid ≈9.1–9.2 cm (≈3.6 in) with erect girth ≈11.7–11.9 cm (≈4.6–4.7 in) ^[1][3]. Report the range and note measurement method when possible; many sources recommend clinicians cite nomograms from the 2015 provider‑measured review for counselling ^[1][5].

7. Competing perspectives and why they matter

Public summaries (Healthline, WebMD, Medical News Today) echo the provider‑measured meta‑analyses and present averages near 5.1 in erect, but popular country‑ranking sites and newer self‑report surveys produce higher or widely varying numbers and sometimes sensational regional rankings; those should be treated cautiously because they mix methods and self‑report ^[10][11][12]. The academic consensus favors examiner‑measured meta‑analyses for accuracy ^[5][2].

8. Bottom line for readers and clinicians

Use examiner‑measured pooled estimates for clinical or educational statements: erect ≈13 cm and flaccid ≈9 cm, with erect circumference ≈11.7–11.9 cm ^[1][3]. Always specify measurement method, acknowledge sampling and bias issues called out in the meta‑analyses, and avoid treating single country lists or self‑reported surveys as equivalent to provider‑measured research ^[6][5].