Vagina size has been more of interest in medical studies and surgery. It has not been an intense subject of study as penis size and shape. It is even a complex subject since the vagina can really vary in size and shape depending on arousal level, during sex depending on penis size and shape, during child birth etc
The length of the vagina is measured from the entrance to the cervix. Cervix is the entrance to the womb. The length is 3 to 4 inches. During sexual arousal, the vagina expands both in length and width considerably, even to getting doubled. This means aroused, vaginas varies anywhere between 6 to 8 inches on average. This means even a well endowed penis can still penetrate the vagina with ease if the lady is fully aroused. However, most vaginal nerves are located around 2 to 3 inches from vagina’s entrance.
Most vaginas are closed when not aroused. When aroused width varies so much and most vaginas have a visible opening. The resulting expansion when something is introduced in the vagina depends on arousal level. Thus vaginas have a tremendous ability to accommodate a well endowed penis as long as the lady is highly aroused. Most ladies who experience pain due to having sex with men who are above average in penis thickness mostly it has to do with lack of sufficient arousal or lubrication.
The vagina almost automatically adapts to the shape of anything introduced into it. Most vaginas, when a woman is standing upright slants backward at around 45 degrees. Most vaginas are wider inside than at the entrance. This is why some ladies experience vaginal flatulence, a situation when the vagina sucks in air and release it later.