5,5 to 6” is average, over 7” is large, over 8” is big and over 9” is huge. Most women are comfortable with 7 to 8” because the vagina can be stretched to this size and soft touching of the cervix can cause strong orgasms, then it becomes painful, but even a cock over 6” can be satisfactory, less than 5” really has no meaning to be put in the pussy, that is not a cock but a kind of male clitoris.