To our knowledge, the research paper named: “Predicting penile size during erection”, and published on 2000 by the International Journal of Impotence research is the only study that provides an average penis girth number. Scientists from the Tel aviv Sourasky medical centre measured the penis girth in arousal state at its base. The same investigator performed all the measurements. he used an ordinary “tumo-meter” to do the measurements of circumference. 70 volunteers from caucasian jewish ethnic origin took part in the study. Penile dimensions were only measured in 55 of them. They came up with an average penis circumference at its base measuring 10.6 cm (4.17 inches) with a standard deviation of 1.6 cm (0.6 inches). For your information average penis circumference was equal to 9.5 cm (3.7 inches) with a standard deviation of 1.5 cm (0.59 inches) at the corona (at the base of the glans).
Practitioners from the cancun lifestyle condom study found that the average penis circumference was equal to 12.63 cm (4.97 inches). However, the lifestyle condom methodology has never been published. Thus, we don’t know where the penis shaft has been measured. Was it at its base, at the mid-shaft or at the corona?
By the way, the wikipedia page dedicated to “human penis size” (sorry no wiki link here. I don’t want to give pagerank to bad information sources) claims that lifestyles study practitioners performed measurements at the penis’ bases, mid-shaft, corona, and averaged it. However, there is no reference of such a methodology description of the manufacturer. By the way, there is also no methodology description for the penis length measurement. It questions the exactitude of the Wikipedia page for human penis size.
So we cannot use the cancun lifestyle candom study as a reference to determine the average penis circumference.