The male reproductive organ generally refers to the penis, which is usually 5 to 6 centimeters long when it is soft and 8 to 12 centimeters long when it is erect. However, the physical development of each man is different, so the specific length of the penis can not be generalized. The penis is an important male sex organ that serves the purposes of sexual intercourse, urination and ejaculation. The length of the penis is usually 5 to 6 centimeters when it is soft and 8 to 12 centimeters when it is erect. If a man’s penis is less than 4 centimeters in length when soft and less than 8 centimeters when erect, he has a short penis, which may be caused by obesity and androgen deficiency. Penis length can be affected by a variety of factors, such as whether the body’s sex hormone secretion is sufficient, genetic factors, and the nutritional status of the organism. If the body does not produce enough testosterone, it may lead to short penis, and the patient is also prone to symptoms such as decreased libido and low sperm quality. If the penis length is within the above mentioned range, it is normal. If the penis is short, it is recommended to visit a urologist to determine the cause.