There are no studies with strong methodology that show knowing a man’s race has any bearing on how large his penis might be. This must be one of the most incorrectly thought beliefs on penis size.
Penile size and the ‘small penis syndrome’
Volume 99, Issue 6, pages 1449–1455, June 2007
The male is often troubled by concerns that his penis is not large enough to satisfy his partner or himself. He is ashamed to have others view his penis, especially in the flaccid state. Such concerns might be unfounded in reality and might be a presentation of social anxiety or some other clinical problem, such as erectile dysfunction. Concern over the size of the penis, when such concern becomes excessive, might present as the ‘small penis syndrome’, an obsessive rumination with compulsive checking rituals, body dysmorphic disorder, or as part of a psychosis. However, it is often a worry that can be described as within the normal experience of many men. Various potential causal factors are considered. A thorough assessment, normalizing the worry and then exploring the treatment options in detail with the man, is essential to allow the matter to be consolidated satisfactorily within the male ego.
More research is required on the effects of race and age on penile length.
People make an assumption you can know a man’s penis by his race. Unfortunately, that is steeped in myth and not facts. Most studies have either not considered race, or studied men of the same race. The few that addressed the issue have done so poorly.
To highlight the problem, the often quoted Kinsey study claimed to show a difference in race penis length but they compared 2770 caucasian men to only 55 men of african descent.