During vaginal intercourse, the penis enters the vagina, which is the middle of three openings in the vulvar area. The vagina is a flexible, muscular canal about 3 to 4 inches deep in a resting state that expands to 4 to 8 inches when aroused. It sits between the urethral opening (above) and the anal opening (below), and it’s the only one of the three designed for penetrative sex.
Three Openings, Three Different Functions
A common source of confusion is that the vulvar area has three separate openings, arranged front to back. Many people aren’t taught this clearly. In a 2020 survey, nearly one in four women misidentified the vagina on a diagram, so if this is new information, you’re far from alone.
Here’s the layout, from front to back:
- Urethral opening: A tiny opening where urine exits the body. The female urethra is only about 1.5 inches long and a few millimeters wide. It is far too small for penetration, and attempting it would cause pain and injury.
- Vaginal opening: Located just below the urethral opening. This is where the penis goes during vaginal sex. It’s also the opening through which menstrual blood exits and babies are born. It’s significantly larger and more flexible than the urethra.
- Anal opening: Located further back, below the vaginal opening. This is part of the digestive tract.
All three openings are close together, which is one reason people find the anatomy confusing. The entire external area is called the vulva, not the vagina. The vagina itself is the internal canal.
How the Vagina Works During Sex
The vagina is built to accommodate penetration. Its walls contain layers of tissue that stretch and expand, and they’re lined with nerve endings that allow you to experience pleasure during arousal. When a person with a vagina becomes aroused, blood flow to the area increases, the vaginal walls produce natural lubrication, and the cervix lifts slightly. All of this makes the canal longer and wider, reducing friction and discomfort.
In a resting state, the vaginal walls rest against each other, so it’s not an open hole. Think of it more like a collapsed tube that opens and stretches as needed. The width changes dramatically between an unaroused and aroused state. This is why foreplay and arousal matter for comfortable sex: without arousal, the vagina is shorter, narrower, and dry, which makes penetration uncomfortable or painful.
Finding the Right Opening
If you’re new to sex, locating the vaginal opening can feel uncertain in the moment, and that’s normal. The vaginal opening sits roughly in the center of the vulvar area, below the clitoris and urethral opening, and above the anus. It’s noticeably lower than most people expect.
A few practical notes: the urethral opening is very small and located near the top of the vulva, closer to the clitoris. You’re unlikely to accidentally penetrate it because it’s simply too tiny. The vaginal opening is larger and more accessible. If you or your partner guide the penis with a hand, alignment becomes much easier. There’s no reason to feel awkward about using your hands during sex to help with positioning.
What About Anal Sex?
Some people engage in anal sex, where the penis enters the anus instead. This is a separate decision that carries different health considerations. The rectal lining is thinner and more fragile than the vaginal lining, which is why it tears more easily. The tissue difference also means sexually transmitted infections pass more readily during anal sex. One study found the risk of HIV transmission per act of unprotected receptive anal intercourse was roughly 3.4%, compared to less than 0.01% per act of vaginal intercourse. Women who had unprotected anal intercourse were about 2.6 times more likely to receive an STI diagnosis than those who only had unprotected vaginal intercourse.
Unlike the vagina, the anus does not self-lubricate, so external lubrication is necessary to prevent tearing. It’s also important never to move from anal contact to vaginal contact without cleaning or changing a condom first, because bacteria from the rectum can cause vaginal and urinary tract infections.
Why This Is Confusing for So Many People
Sex education in many places covers reproduction but glosses over practical anatomy. The word “vagina” is routinely used to describe the entire vulvar area, which makes it harder to understand that the vagina is one specific internal canal with a specific opening. When people say “vagina” but mean “everything down there,” the actual anatomy gets lost.
Knowing where things are and how they work makes sex safer, more comfortable, and less stressful for everyone involved. If you’re unsure about your own or a partner’s anatomy, there’s no shame in looking at a labeled diagram or simply exploring with your hands in a low-pressure setting.