Patient's question:
How long and thick is the normal penis of a man?Doctor's answer:
What is the standard size of the penis?How can a penis be considered abnormal? If the penis is slightly smaller, will it affect normal sexual life? That is to say, can it make the wife feel pleasure?
Methods for measuring penis length: one is to measure in a flaccid state, and the other is to measure the change during an erect state. The room temperature should be around 25°C, and after calming down and resting appropriately, the penis should be held flat with one end of a hard ruler slightly pressed against the pubic symphysis, compressing the subcutaneous fat layer as much as possible. The other end should be aligned with the urethral meatus of the glans penis, and the number read is the normal length of the penis. Then, use a tape measure to measure the circumference of the penile shaft 1 cm away from the corona.
The penis, like height, weight, and facial features, varies greatly among individuals, with differences in length and thickness. Shi Chengli measured the penis size of 1,412 healthy Chinese young men and the erect length of 126 healthy men. The results showed that the longest normal length was 14.5 cm, the shortest 4 cm, and the average 8.375 cm; the maximum circumference was 12 cm, the minimum 4.5 cm, and the average 8.3 cm. During erection, the longest was 16 cm, the shortest 9 cm, and the average 12 cm; the maximum erect circumference was 14 cm, the minimum 8 cm, and the average 10.75 cm. Liu Guozhen et al. surveyed 1,000 normal adult men and found that the normal length ranged from 4.9 to 8.6 cm, with an average of 6.55 cm, the longest being 10.6 cm, and the shortest 3.7 cm. Wu Weicheng et al. measured 2,547 male college students aged 16–40 and found an average length of 7.43 cm and an average circumference of 8.17 cm. The average penile stretch was 13.34 cm, similar to the calculated erect length of 13.08 cm, suggesting that stretch can represent the post-erect length. It is evident that the results of different authors vary, and these results are also influenced by region and ethnicity. Additionally, a person's penis length is not constant under normal conditions; it may shorten during stress, cold, or severe fatigue. Moreover, the methods of measurement themselves differ significantly, making it difficult to judge whether a penis is normal solely based on length. Therefore, these figures are only for reference and should not be rigidly compared with one's own length. Clinicians are also reluctant to judge normality based on penis length. As long as normal sexual intercourse can be performed and the ability to reproduce is maintained, it is considered normal. Otherwise, this family line would have been eliminated long ago.
So, what constitutes a truly small penis? A penis shorter than 2.5 cm before puberty and shorter than 5 cm after puberty, with abnormal development and no erectile function; especially when secondary sexual characteristics are underdeveloped, sexual dysfunction, infertility, and no sperm are present, it can be considered abnormal penis development. The causes of true micropenis include:
(1) High gonadotropin-dependent hypogonadism, where the hypothalamus and pituitary are normal but the testes are diseased, unable to produce hormones and sperm.
(2) Hypogonadism due to low gonadotropin, where the hypothalamus and pituitary are affected, unable to secrete testosterone. These two conditions have been described in this book.
(3) Partial androgen insensitivity syndrome, where the penis is insensitive to androgens, with normal testosterone levels but abnormal secondary sexual characteristics, possibly even hypospadias.
(4) Idiopathic micropenis, with unknown causes.
To further explain the factors or causes of a large or small penis, let us revisit the process of penis development. For convenience, we divide it into four stages:
(1) Weeks 10–12 of pregnancy, when the penis has just differentiated and is only 3.5 mm long, influenced by testosterone produced by hCG from the placenta.
(2) Mid to late pregnancy (6 months), when the penis grows rapidly, reaching 2.5–3.5 cm at birth, as the fetal pituitary begins to secrete LH and FSH.
(3) From birth to pre-puberty (around age 7), penis growth is slow due to the slow development of the hypothalamus and pituitary and low testosterone levels.
(4) After puberty, the pituitary and testicular hormones are secreted vigorously, and the penis grows rapidly, reaching adult size in about 5 years, increasing in length and thickness. When elderly hormone levels significantly decrease or after surgical castration, the penis may undergo secondary atrophy. If secondary erectile dysfunction persists for many years without sexual contact, it may lead to pathological atrophy, which is not the general issue of "use it or lose it" but rather the result of degenerative changes in smooth muscle fibers.
In summary, the differentiation and development of the penis rely entirely on the body's testosterone levels. If testosterone secretion is insufficient during weeks 6–9 of pregnancy, penis development will be slower than normal, and the penis will be smaller at birth.