How is the length of the penis measured

Patient's question:

How is the length of the penis measured, and what is considered ideal, and why? Thank you

Doctor's answer:

Hello: For Chinese people, a penis is considered small if its length in the erect state (not erect is not counted) is shorter than 12 centimeters and its diameter is less than 3.1 centimeters, and it is considered normal if it exceeds this. The shortness of the penis is affected by the following factors.
　　The influence of genetic genes is the most fundamental;
　　Improper medication during pregnancy in the mother's body affects the secretion of male hormones, resulting in insufficient male; lack of nutrients and elements for strong sexual function, forming congenital developmental malformation;
　　During adolescence, insufficient intake of zinc elements, male hormones, vitamin E, and related protein nutrients, and lack of postnatal energy supplementation, fails to promote the growth of sexual organs;
　　Excessive cold in the body, fear of cold, insufficient yang energy in the body, making the penis unable to fully protrude, with part retracted into the abdomen;
　　Excessive sexual activity, physical weakness, or frequent masturbation during adolescence, leaving no energy for the kidneys to develop sexual organs during development, resulting in a small penis;
　　Suffering from conditions such as orchitis, cryptorchidism, incomplete testicular development, and endocrine imbalance, with insufficient male hormones;
　　Excessive foreskin, lack of necessary space for growth, hindering the development and growth of the penis.

The penis of a normal person is the male copulatory organ, with dual functions of urination and ejaculation. The penis can be divided into three parts: the head, the body, and the root. The posterior part of the penis is the "penis root," the middle part is the "penis body," and the anterior part of the body is the "penis head." The penis head is rich in nerve endings and is the main erogenous zone for males, usually covered by the foreskin. The penis foreskin is the annular fold surrounding the penis head. In