A man’s bottom generally refers to the penis. For men in China, the average length of the penis is about 8.8cm in the resting state, i.e., the soft state, and about 12.9cm in the erect state. This length refers to the position from the root of the penis to the opening of the urethra, which is measured from the pubic symphysis to the opening of the urethra, while trying to exclude subcutaneous fat as well as surrounding tissues. The length of the penis varies according to genetics and individual constitution. If the penis is still able to have normal sex after erection, a shorter length is not a cause for too much stress and anxiety. However, if the penis length becomes fixed in adulthood and then affects your sex life, you should consult a doctor.