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Which studies report 5th and 95th percentile penis lengths and what sample sizes do they use?
Executive Summary
Multiple peer-reviewed studies and systematic reviews report 5th and 95th percentile penis lengths but they vary by measurement state (flaccid, stretched, erect), sample size and geography. The most-cited nomogram study analyzed up to 15,521 men and provides the clearest percentile estimates (5th/95th) for flaccid and erect lengths, while smaller single-country studies report differing percentiles and caution about representativeness [1] [2]. These differences reflect measurement methods, sample composition and reporting choices rather than a single universal standard.
1. The study that most often supplies percentiles — large nomograms that clinicians cite
A BJU International systematic review and nomogram project led by Veale and colleagues pooled measurements from multiple studies and reports nomograms built on up to 15,521 men, giving the most comprehensive percentile estimates commonly used in clinical contexts. The review gives mean and standard deviation values for flaccid pendulous, stretched and erect lengths and, in reconstructed nomograms, yields approximate 5th and 95th percentiles: flaccid roughly 6.6 cm (5th) to 13.1 cm (95th) and erect roughly 10.4 cm (5th) to 16.4 cm (95th) [1] [3]. The study’s largest subsamples were 10,704 men for flaccid length and 14,160 for stretched length, while the erect-length dataset was much smaller at 692 men, and the authors emphasize standardized measurement methods to support these percentiles [1] [3]. These sample sizes make the nomograms the primary reference for percentile ranges.
2. Smaller, single-country studies that report percentiles and how they differ
Country-specific research yields different 5th/95th figures and often smaller samples that limit generalisability. For example, a 2017 study of 223 Iraqi men reports flaccid 5th/95th roughly 7 cm / 12 cm and stretched 5th/95th roughly 10 cm / 15 cm, noting age-related variation and that the sample may not represent the entire adult male population of Iraq [2]. These single-cohort studies frequently provide detailed age-stratified percentiles and highlight within-population variability, but their sample sizes (e.g., 223) are far smaller than pooled nomograms and so carry larger sampling uncertainty when used as universal reference values [2].
3. Recent meta-analyses and gaps — what the big aggregations report and what they omit
More recent systematic reviews and meta-analyses expand geographic scope and sample counts but do not always report explicit 5th/95th percentiles. A 2024/2025-style review aggregated 33 studies with 36,883 patients and reported mean regional differences (stretched length largest in Americans) but did not provide explicit 5th and 95th percentile values, limiting immediate clinical interpretation from a percentile perspective [4]. The 2014–2015 nomogram paper does provide reconstructed percentiles, but notable gaps remain: erect-length data were based on a relatively small subsample (692 men), and several meta-analyses prioritize means over percentile cutoffs, leaving clinicians to infer percentiles from SDs or nomograms [3] [5].
4. Why percentiles differ: measurement state, methods and sample composition
Percentile estimates vary because studies measure different states (flaccid, stretched, erect), use different measurement protocols, and draw from samples with differing ages, ethnicities and recruitment methods. The nomogram study documents larger sample sizes for flaccid and stretched measurements and a much smaller erect sample, which explains why erect percentiles are less robust and more variable across reports [1]. Single-country studies can show higher or lower percentiles due to population-specific traits or small-sample noise; meta-analyses that aggregate across regions reduce random variation but can obscure meaningful regional differences that some studies highlight [2] [4].
5. Practical takeaways for clinicians, researchers and readers seeking percentiles
For immediate percentile references, use the nomogram-based estimates from the pooled 2014–2015 systematic review (flaccid ~5th 6.6 cm / 95th 13.1 cm; erect ~5th 10.4 cm / 95th 16.4 cm) while noting that erect estimates are based on far fewer observations and that regional studies report different cutoffs [1]. Smaller single-country studies are useful for local counseling (for example, the Iraqi cohort of 223 men) but should not replace pooled nomograms when seeking broader population percentiles [2]. Where meta-analyses report only means, clinicians must either consult nomograms or derive percentile bounds using reported SDs and sample distributions, keeping in mind methodological heterogeneity across studies [4] [5].
6. Bottom line: which studies to cite for 5th and 95th percentiles
Cite the BJU International nomogram work (Veale et al.) as the primary source for commonly cited 5th and 95th percentile penis lengths because it aggregates large samples and provides reconstructed percentiles; supplement with country-specific studies like the 2017 Iraqi cohort for local context, and treat large-region meta-analyses as informative for mean differences but not as a direct percentile source unless they explicitly report percentiles [1] [2] [4]. Always state which measurement state (flaccid, stretched, erect) and the sample size underlying the percentiles when quoting these ranges.