A study was conducted in America that compared penile length with a whole bunch of demographic facts, such as race, sexual orientation, income, education, etc.

Here is the link to the study:

https://www.ncbi.nlm.nih.gov/pubmed/23841855

NON-PAYWALLED VERSION:

https://www.icopona.nz/content/Erect%20Penis%20Study%20-%20Herbenick%20et%20al%202014%20J%20Sex%20Med.pdf

It is quite an interesting study. To date, I believe it is the most comprehensive, largest, and as far as I am aware only study ever undertaken to measure penis-size (that wasn't self-reported) and its relationship to race.

According to the study, here are the average measured penis sizes by length in centimeters from largest to smallest. (Remember this is NOT self-reported)

Native Hawaiian/Other Pacific-Islander : 14.88cm
Black/African American : 14.66cm
White/Caucasian : 14.18cm
Asian American : 14.14cm
Hispanic/Latino : 14.13cm
Other : 13.79cm
American Indian : 12.86cm