First of all, you should choose to measure after erection so that the conclusions drawn are meaningful. For example, after taking a shower, rest a little, when the penis is more relaxed. Prepare a tape measure. After an erection, place the end of the tape measure at the root directly above the penis, then gently press the penis with one hand, press on top of the tape measure, and read the scale. If you want to measure the circumference of the penis, you should put the tape measure over the middle of the penis. Because the penis is not a regular cylinder, some people have the thickest root, while others have a larger circumference the closer they are to the glans. Generally, the thickness in the middle is more objective. It is normal for the penis to be 11-15 cm in length when erect and around 10 cm in circumference. Regular measurement of the girth and length of the penis can give an idea of the health level of the male reproductive system. If the circumference of the penis becomes larger and the elasticity decreases, we should suspect if it is sclerosis; if the erection length becomes shorter and the circumference shrinks, we should suspect if there is a problem with erectile function. Commentary: 1. When measuring, the end of the ruler near the root of the penis should be forced in the direction of the pubic bone to push away the local subcutaneous fat. 2. The normal value of erect penis length mentioned in the article is based on the standard of men in western countries, and may not be suitable for Chinese men. The erect penis length and circumference of Chinese men are generally smaller than those of men in Western countries. 3, many men demand too much for their penis length and circumference, and try every possible way to beg doctors to do surgery for them. Many of these patients have normal penis size, and clinically this pathology is called “small penis syndrome”.