What are the average flaccid and stretched penile lengths for Tanner stage I through V?
Executive summary
Clinical staging of male puberty (Tanner I–V) correlates with predictable increases in penile size, but precise average values for flaccid and stretched penile length (SPL) by Tanner stage are heterogeneous in the literature and vary by measurement method and population; existing sources give useful anchors—prepubertal flaccid length ~1–3 cm, early penile lengthening around 6 cm (stage III), further lengthening to roughly 10 cm by late puberty, and adult/Stage V values that approach typical adult erect lengths reported near 15 cm in some series—but comprehensive, standardized stage-by-stage flaccid and SPL averages are limited in the publicly available reports [1] [2] [3].
1. Tanner staging and what it measures: the clinical framework
The Tanner scale rates external genital and pubic hair development in five stages and is widely used as the clinical gold standard for pubertal assessment when performed by trained examiners; for boys the genital component explicitly includes penile and testicular changes, so penile length progresses across stages as part of that genital score [4] [5] [6].
2. What published clinical descriptions say about penile length by stage
Classical descriptive sources and teaching materials link Stage I (prepubertal) to a small, non-hanging penis typically in the 1–3 cm range, Stage II to minimal change with scrotal/testicular enlargement and little penile length increase, Stage III to a clear lengthening of the penis with values reported around 6 cm for lengthening at this stage, Stage IV to further penile length increase toward about 10 cm, and Stage V to adult size—textbooks and synthesis pages cite these approximate penile-length landmarks [1] [2] [6].
3. Stretched penile length (SPL) data and population studies
Cross‑sectional studies that actually measured SPL and linked it to Tanner stage exist but differ by population; for example, a study from western Maharashtra measured SPL across ages and reported mean SPLs correlated with genital stages (the paper states that mean SPL and testicular measures are tabulated by Tanner stage), but the summary text does not reproduce stage-by-stage numeric means in the abstract so those detailed figures require consulting the article’s tables directly [3]. Broader adolescent cohorts and specialty studies have also measured SPL and shown a stepwise increase with advancing pubertal stage, but values and centiles vary by region and methodology [7] [3].
4. How to interpret “flaccid” versus “stretched” figures and measurement caveats
“Flaccid” measurements are inherently variable with temperature, anxiety and relaxation, while SPL (gentle traction along the penile shaft until resistance) is more reproducible and commonly used in pediatric normative work and micropenis definitions; many authoritative discussions therefore emphasize SPL rather than flaccid length for comparisons, and some classic Tanner-derived descriptions report penis “length” in anatomical teaching that may not state whether it is flaccid, stretched, or erect—limiting direct translation [3] [8].
5. Bottom line and limits of current reporting
A practical synthesis from the available sources: Tanner I flaccid length roughly 1–3 cm; Tanner II little change from that baseline; Tanner III SPL/length near ~6 cm; Tanner IV length near ~10 cm; and Tanner V approaching mature adult values (with some references citing adult erect lengths ~15 cm as a comparative anchor), but precise, universally generalizable average flaccid and SPL numbers per Tanner stage are not fully standardized across populations and require consulting original measurement studies (for example the western Maharashtra SPL dataset and other SPL-by-stage studies) to obtain exact stage means and SDs for a given population [1] [2] [3] [7]. Alternative interpretations note that testicular volume and penile/scrotal change can be discordant in some clinical contexts, prompting experts to separate penis/scrotal staging from testicular volume in nuanced assessments [8].