Baseline distributions: Veale D, et al. Am I normal? A systematic review and construction of nomograms for flaccid and erect penis length and circumference in up to 15 521 men. BJU Int. 2015;115(6):978–986. (systematic review, n = 15,521).
Country data: compiled from public aggregators (e.g. WorldData.info) covering 134 countries. Methodology and sample quality vary widely: low reliability, indicative estimates only, not peer-reviewed.
Percentiles assume a normal distribution. Where a country provides no standard deviation, the erect SDs from the global review (1.66 cm length, 1.10 cm girth) are used as fallback.
Size tiers classify values by standard-deviation bands from the active baseline average: micro (below −2 SD), modest (−2 to −1 SD), average (−1 to +1 SD), large (+1 to +2 SD), huge (+2 to +3 SD) and elite (above +3 SD).