Which studies report penis size percentiles and sample sizes?
Executive summary
Three types of studies report penis-size percentiles and sample sizes: large systematic reviews and nomogram-building meta-analyses that pool many clinic-measured studies, country-level prospective studies that publish percentile tables for their samples, and web- or survey-based efforts that provide percentile charts from self-measured or self-reported data; the best-cited clinic-based nomogram pools 20 studies with a combined sample of 15,521 men and many newer reviews extend and critique that work [1] [2] [3].
1. The headline nomogram — “Am I Normal?” and its pooled sample
The most frequently cited clinic-based source that explicitly provides percentiles and sample sizes is the systematic review and nomogram study often summarized as “Am I Normal?”, which pooled data from 20 studies across 16 countries to construct percentile charts for flaccid, stretched and erect length and circumference with a cumulative pooled sample of 15,521 men [3] [2] [1].
2. What those pooled studies required and reported about minimum sample sizes
Veale and colleagues’ systematic approach required that measurements be made by a health professional using a standardized protocol and that individual studies include at least 50 participants, a threshold built into eligibility criteria so that percentiles would not rest on very small samples [3] [1].
3. National and regional studies that publish percentiles and their samples
Several country- or region-specific clinical series publish percentile cutoffs and report sample sizes: an Argentine prospective study measured penile dimensions in 800 men and explicitly defined micropenis as measurements at or below the 5th percentile for that sample (flaccid ≤7 cm; stretched ≤10 cm) while urging caution about representativeness [4]. Pediatric and adolescent growth-curve work from Chongqing, China, produced age-specific smoothed percentile curves (3rd–97th) for penile length and diameter based on 3,033 boys, demonstrating that large, single-country datasets also produce usable percentile charts [5].
4. Systematic reviews and meta-analyses that update percentiles and sample reporting through 2022–2024
Beyond the 2015 nomogram, later systematic reviews and meta-analyses have re-examined the literature: a 2023 temporal review and a 2024 WHO-region meta-analysis screened studies for investigator-measured data and required sample reporting (some reviews accepted studies with a lower cutoff such as n ≥10), and both papers note that erect measurements and regional comparisons are limited by relatively few studies and modest per-study sample sizes [6] [7].
5. Non-clinical surveys and online percentile calculators — large numbers, different methods
Large online surveys and tools also produce percentile tables but use self-measured or self-reported data and different inclusion rules: an independent size-survey site reports percentiles from 2,545 participating adults, and web calculators aggregate literature-based expectations to estimate rarity, but these methods diverge from clinician-measured studies and carry different biases [8] [9].
6. How the reported percentiles are presented in media and secondary sources
Media coverage and health portals often translate nomogram outputs into familiar percentile thresholds — for example, reporting that an erect length of ~10 cm corresponds to roughly the 5th percentile and that common ranges around means capture 68% and 95% bands — but such pieces typically rely on the pooled nomogram and reviews rather than new raw datasets [10] [11] [12].
7. Limits, heterogeneity, and how to read percentile claims
All of these sources warn that percentiles depend on measurement protocol (pubic bone to glans, compression of fat pad), population sampled, and whether measurements were clinician- or self-taken; pooled nomograms improve precision by combining studies but still underline heterogeneity and smaller sample counts for erect measurements, meaning percentile precision varies by measurement type and region [3] [2] [7].
Bottom line
For clinician-measured percentiles and transparent sample sizes, the primary reference is the pooled nomogram (≈20 studies, pooled n ≈15,521) and follow-up systematic reviews/meta-analyses that report per-study sample sizes and sometimes stricter inclusion cutoffs; large single-country clinical series (e.g., n=800 in Argentina; n=3,033 pediatric sample in Chongqing) provide alternative percentile charts, while online surveys and calculators offer larger-sample percentiles but with different and sometimes weaker measurement validity [1] [2] [4] [5] [8] [9].