Can one calculate the vacuum pressure created inside a bottle when pouring liquid from it?
Glass bottle 38mm diameter orifice
No vacuum is created. Liquid will not flow out unless air bubble goes inside and equals the atmospheric pressure. (Unless one is taking about a bottle talker than the barometric height, about 1 meter if the liquid is mercury.) The bottle opening does not come into the picture. A wider opening makes it easier for the air bubble to enter.