Well, yes, vaginas are made to stretch to accomodate babies, which are much larger that a penis. However there are many other factors involved. I believe a hormone that is released during birth also increases the elasticity of the vagina to help it stretch more than normal. Also there is dilation to factor in. Now if you are dilated to let's say 5, that would be 5 cm, which is approximately 2 inches, since ~2.54 cm = 1 inch. Now of course you can easily dilate to more than that and get up to 10 cm, which is about 4 inches. I have not met any woman who's vagina is normally anywhere close to that size normally. Have you?