The belief that penis size varies according to race is not supported by scientific evidence.[6][27] A 2005 study reported that "there is no scientific background to support the alleged 'oversized' penis in black people".[28]
A study of 253 men from Tanzania found that the average stretched flaccid penis length of Tanzanian males is 11 cm (4.53 inches) long, smaller than the worldwide average, stretched flaccid penis length of 13.24 cm (5.21 inches), and average erect penis length of 13.12 cm (5.17 inches).[29]
A study of 115 men from Nigeria found that the average flaccid stretched penis length of Nigerian males is 13.37 cm (5.26 inches) long, which is near identical to the worldwide average, stretched flaccid penis length of 13.24 cm (5.21 inches) and average erect penis length of 13.12 cm (5.17 inches).[30] A 2015 systematic review of 15,521 men found "no indications of differences in racial variability", and stated that it was not possible to draw any conclusions about size and race from the available literature and that further research needed to be conducted.[1]
According to Aaron Spitz, a urologist, many websites and studies promoting variation of penis size between races use unscientific methods of collecting information and often ignore contradictory evidence. He concludes that "when you really take a good look at the naked data, there’s not a whole lot there [showing racial variation in penis size]."[31]
https://en.wikipedia.org/wiki/Human_penis_size