There is no such thing as a vaginal hood...the vagina is inside the vuvla is outside. The vuvla is the lips and so on that is outside. Now this includes the clitoris which does have a hood. There really isnt an average because we are all different. I do suggest that a search for female anatomy might be helpful to you.
DS 13 yr
DS 8 yr (3+ yrs ttc)
TTC #3 since 01/02
Just_me_again, when you look at your pubic area you can se the two mayor labia (lips) usually very close together, also you can see a little protruding between you mayor labia which is you clitoreal area. If you split the mayor labia you will see the clitoris, and the minor labia. The clitoris itself, use to be replegated under a little hood (clitoris prepuscio) and under it a frenulum. Also you will be able to see your urinari meatus (the small hole from where your pee goes out)
By opening the ninor labia, you wil find the entrance of your vagina (vaginal vestibule) and you hymem.
Once you have sex and are penetrated you hymen will look torn, hence you had loose your virginity.
Try to find a good, clear and well drawn atlas of women pubic area. There are many on the web. Is very important for young people to know what you have, where is and how it works. If you make relations by thinking on the matter you will understand many of the questions you have. For the ones you cannot understand you can ask, but you has to do your homework first.
I guess it's about 1/4 to 1/2 an inch in lenght perhaps a bit longer but depends on how tall and big id the girl, I have never measured so I can tell you from my tactil experience. Usually covers completely the clitoris until you get sexually aroused when the clitoris becomes erect and extremely sensitive. As mater of fact, in there, there are about 8000 more nerves terminals than in the corresponding part of men's penis.
Actually, illustrated anatomy books are notorious for drawing the clitoris and hood extra small. And the sizes DoveTail gives are more like the size of the clitoris, the hood it self can be much longer going up farther and fading away.