I dig this up from my post a few months ago....
The "G" spot is usually located only 2-3 inches inside the vagina on the upper side. (closer to her belly)
Size has NOTHING to do with it, you can find it with one finger only two knuckles in. Really try with your fingers before your dick.
Go in with your finger and apply gentle upward pressure toward the belly. It usually feels like a small rough patch of tissue that gets rougher and swells a bit as you stimulate it. Move your finger toward you in a "come here" kind of move. Your wrist will get tired quickly, but ya gotta practice.