There is no doubt that whether the penis can be fully erected is an important sign of good or bad male sexual physiological activity. In other words, a full erection of the penis is a must in order to successfully complete a couple’s life. So what kind of penis is hard enough? Generally, the hardness of the erect penis can be divided into 4 levels: level 1, the penis is swollen but not hard, like tofu; level 2, slightly hard, but not enough to insert into the vagina, like a peeled banana; level 3, the penis is hard enough to insert into the vagina, but not completely hard, like a banana with skin; level 4, fully erect and hard, like a small cucumber. Only level 4 hardness can make both partners fully enjoy the pleasure of sex. This method is simple, but the result is often inaccurate because it is your own subjective feeling. We can use some instruments to make objective measurements. There are more measurement methods, with the nocturnal erection test being the most commonly used. Generally speaking, the number of nocturnal erections increases after puberty, averaging 3 to 6 times per night, lasting 20 to 40 minutes each time, for a total of about 100 minutes, and even after reaching the age of 60 to 65, there are still cumulative erections of 1 hour to 1.5 hours per night.