"Just under three thousand (2,936) men took part in a DUREX survey – most of them under 25 – from all over the world. They self-reported there erect length and circumference. Both length and circumference vary quite widely but in each case there is an average value and in this survey they were 163 mm (6.4 inches) for erect length and 133 mm (5.2 inches) for erect circumference. "
This is typical of surveys released publicly with absolutely no scientific background nor interest. Why then? It is unclear why manufacturers would release such information.
Below you will find a collection of true scientific studies, ie. anybody can reproduce it, following the exact same protocols.
* Are included in the scientific average only the studies where the medical staff did the measuring or ensured a proper training.
** The average erect circumference was extrapolated from the measured erect width considering the penis is a cylinder.
So basically, true scientific studies, where medical staff is conducting, training and often performing the measurement, come short of up to 1cm (0.4in) compared with non scientific internet surveys.
NB: I didn't report data for length as it is not really relevant for choosing the right condom. As an example though, the Wessel Study came up with the following results: Erect length: 128.9mm (sd 29.1mm), fat pad : 28.5mm (sd 15.9mm), Functional erect length (Erect length non pubic bone pressed plus fat pad): 157.4mm (sd 26.2mm). This last result is consistent with the Kinsey data. To finish with erect penis length, the average (obtained by pressing the ruler on the pubic bone) from the scientific studies* above, is 147.64mm (sd 19.78mm).
So the real average erect circumference, or average erect penis girth, is around 121-123 mm.
See here for further details:
Wessells H, Lue TF, McAninch JW. Penile length in the flaccid and erect states: guidelines for penile augmentation. J Urol 1996; 156: 995-997.
Janssen. "Penile Circumference Variability - in a Dutch Sample (1994)". Faculty of Psychology University of Amsterdam.
Schneider T, Sperling H, Lummen G, Syllwasschy J, Rubben H. "Does penile size in younger men cause problems in condom use? A prospective measurement of penile dimensions in 111 young and 32 older men". Urology 2001; 57: 314-318.
da Ros C. "Caucasian penis: what is the normal size?". J Urol 1994; 151: 323A.
Richard Harding, M.Sc. and Susan E. Golombok, Ph.D."Test-Retest Reliability of the Measurement of Penile Dimensions in a Sample of Gay Men"
Penile Size and Penile Enlargement Surgery: A Review: Penile Size