Average penis girth in the US

1. Why “average” varies: measurement methods matter

Clinical measurements taken by health professionals using standardized protocols (pressing the pubic fat pad, measuring mid‑shaft girth) are the basis for the widely cited 2015 review and give the lower girth estimates (erect 11.66 cm / 4.59 in; flaccid 9.31 cm / 3.67–3.7 in) ^{[1] [2]}. By contrast, studies that rely on self‑measurement or online self‑reporting tend to report larger averages — for example, an online U.S. sample of 1,661 men reported average erect girth ≈12.2 cm (4.8 in) ^[3]. The difference reflects measurement bias, volunteer bias and variability in how participants achieve erections for measurement ^{[5] [1]}.

2. The strongest pooled evidence: what the 2015 review found

A multi‑study synthesis published in BJU International pooled measurements from up to 15,521 men and reported average flaccid circumference about 9.31 cm (3.67 in) and erect circumference about 11.66 cm (4.59 in) using clinician measurements and standard methods ^{[1] [2]}. Science and major medical summaries repeat these numbers as the most methodologically rigorous baseline ^{[6] [7]}.

3. U.S.‑specific and survey studies: higher numbers, different caveats

U.S. surveys and some single studies often show higher average girths. For instance, the Indiana University study using self‑measures for condom fitting reported average erect girth ≈12.2 cm (4.8 in) in a 1,661‑person U.S. sample ^[3]. Medical News Today and other outlets cite preference studies where women selected somewhat larger circumferences (≈12.2–12.7 cm / 4.8–5.0 in) as “ideal” for long‑term or one‑time partners — but those are preference, not population‑average, data ^{[4] [8]}.

4. Why context and sampling bias matter for interpretation

Researchers warn about biases: self‑reported data and online volunteers can inflate averages because men with larger sizes may be more willing to report, or because measurement techniques differ ^{[1] [5]}. The pooled clinical studies attempted to reduce such biases by including only studies with standard procedures and excluding men with erectile dysfunction or anatomical abnormalities ^[2].

5. What people care about — preference vs. population

Separate from “average” is what partners prefer: a 2015 study using 3‑D models found women’s preferred erect girths around 12.2–12.7 cm (4.8–5.0 in), slightly above the pooled clinical average ^[8]. Media stories and some health sites highlight these preference numbers alongside averages, which can create the impression the population average is higher than clinical measurements indicate ^{[4] [5]}.

6. Reporting caveats and contested claims

Some sources present one‑off or state‑level rankings and self‑reported national averages (e.g., websites compiling self‑reported U.S. averages or rankings by state) that are not peer‑reviewed and should be treated cautiously; they can conflict with clinician‑measured findings ^[9]. Wikipedia and medical summaries also synthesize the 2015 review numbers but note that self‑measurement studies show inflated values, reinforcing methodological explanations for discrepancies ^[1].

7. Bottom line for a U.S. reader

Available clinician‑measured compilations — considered the more reliable standard — give an erect girth near 11.66 cm (4.59 in) and flaccid girth near 9.31 cm (3.66–3.7 in) ^{[1] [2]}. U.S. self‑report studies often report higher figures (around 12.2 cm / 4.8 in), but those are affected by self‑measurement and sampling biases and therefore diverge from the pooled clinical results ^{[3] [4]}.

Limitations: available sources do not mention recent (post‑2015) large clinician‑measured U.S. national surveys that might change these pooled estimates; much reporting combines clinical averages and preference/survey numbers without always clarifying method ^{[1] [8]}.