Data regarding the size of the adult penis is of great importance to both clinicians and researchers. Currently, there is no consensus regarding the preferred method for the evaluation of penile size. Various and conflicting methods are reported in the literature. We review the data on measurement methods of the flaccid, stretched, and erected penis with the aim of constructing a recommendation for best practice. A systematic search for articles on penile length and girth measurement techniques was performed using PubMed, Google Scholar, and Cochran Library. Only peer-reviewed articles published in English before August 2018 were reviewed. All authors evaluated the methods and results sections presented in each publication. Relevant, demonstrative publications are reported in this review. We did not find definitive evidence favoring one measuring method over the other. Therefore, we advocate the use of our recommendations for penile size measurement in future publications.