I know this does not really matter but how far are the nerve endings of a woman's vagina when it comes to sexual pleasure? I heard that it is only the first couple of inches that matter and that anything more than that is just a bunch of wasted space if you happen to have a larger penis. I heard that the first 3 to 4 inches is what really matters the most and anything bigger than that does not provide more pleasure to her. Is this information correct?
Most of the nerve endings involved in sexual stimulation in a woman are in the clitoris. This is a small pea size organ that is at the top of the vulva, inside the outer vulva, but outside the inner vulva. Though the clitoris appears small externally, internally there is connective tissue to the inner vulva and an area of the vagina about an inch or so internally at the top of the vagina.
The vagina itself doesn't have many nerve endings, almost all the stimulation from sex comes from the various connections to the clitoris being pulled on during sex. Like the glans at the end of the male penis, the clitoris is so highly sensitive to touch that direct touch can be perceived as painful. It is the indirect touch or well lubricated touches that feel the most pleasurable.
Notice that the location of the clitoris means it isn't directly involved with the penis during intercourse. Direct stimulation comes more during foreplay, from the pubic hairs of the male, and movement of the groins when in contact.
Understanding this, then it should be clear that the length of a man's penis has little to do a woman's feelings of pleasure. It is the movement, pushing and pulling on the inner vulva and the vagina, that creates pleasurable feelings. What surprises most men is that a man with an above average penis length is at a disadvantage. He cannot insert his penis fully to the point that his groin rubs against his wife's because the penis bumping against the cervix at the other end of the vagina is painful to the woman. Since the glans of the penis is the widest point, it is the movement of the penis as it is first entering and exiting that gives the most stimulation. The rest of the movement in gives some additional pull on the clitoris through the indirect connections, but not as much as the movement near the entrance. A woman is able to increase her pleasure by learning to squeeze the muscles at the entrance of the vagina so that the penis is gripped more tightly. Since these are not muscles one normally moves conscientiously, it can take a woman time to figure out how it is done.
A wider penis than normal does provide more tug on the vulva and vagina, but here the woman must first adapt to her husband's penis. The vagina has to stretch to accommodate the penis, and like all stretches, the initial set are usually uncomfortable or even painful. A woman can also adapt to a longer penis because the uterus tilts when the woman is sexually aroused, causing the vagina to lengthen. But this too takes time for the wife's body to adjust and learn how much tilt is optimal for sex.