Is size in the eye of the beholder? Visual estimation of penis size among transgender and cisgender people and implications for genital gender-affirming surgery and sexual medicine.

Background: Transgender men (TM) seeking gender-affirming phalloplasty and transgender women (TW) seeking vaginoplasty and desiring insertive intercourse must consider penis size. Evidence has shown that, at least among cisgender men (CM), penile dimensions tend to be poorly estimated. In transgender patients desiring gender-affirming surgery, inaccuracy in estimation of penis dimensions may lead to unnecessary morbidity: for TW, trauma to the neovagina; for TM with excess girth, an inability to insert. Studies on the accuracy with which transgender and cisgender patients estimate penis size are limited.

Aim: To assess the degree of accuracy with which CM and CW, as well as TM and TW, visually estimate the size of the human penis, including length, width, and girth.

Methods: There were 142 participants included (25 TM, 47 TW, 30 CM, and 40 CW; net mean ± SD age, 36.6 ± 11.2 years). Participants were shown these models and asked to estimate length, width, and midshaft girth by visual inspection of 6 realistic models of a penis and scrotum of varying lengths and widths. We evaluated the accuracy of the visual measurements by comparing mean perceived dimensions with the actual dimensions of each model.

Outcomes: We used a multivariate model of all 3 bias dimensions to test for differences in average bias among gender groups (CM, CW, TM, and TW).

Results: TM significantly overestimated length across the longest models. TW significantly overestimated length in the longer 3 models. All groups except for TM significantly underestimated girth in at least 1 model. No groups significantly underestimated width. CM, CW, and TM significantly overestimated width in all 6 models.

Clinical Implications: When transgender patients use numbers to express penis size (either in neophallus or vaginal depth based on perceived partner size), the result is likely to be larger than expected. Use of realistic penis models as a decision-making tool may help manage patient expectations and surgery decision making preoperatively and improve postoperative patient satisfaction and safety.

Strengths And Limitations: To our knowledge, this is the first study to assess visual estimation in penis size in TM and CM, as well as TW and CW. The penile models in our study were shown side by side and in the flaccid state despite having dimensions more consistent with an erect penis, which may have influenced estimations across all dimensions.

Conclusion: Men and women (cisgender and transgender) tend to significantly overestimate penis length and width.