This video is actually very good comparison in size, since both 3 and black Y were parked almost in a straight line, we can see from 0'56" that Y's wheelbase is at least one inches longer than 3, and about one inch wider as well. Y is more like mini X than 'just' a bigger 3 now. I hope they will use UI from cyber truck in Y so it is more like next-gen instead of simple upgrade from 3.
Model Y does seem to have longer wheelbase..... If you pause video at .53 seconds you can clearly see rear wheels on the Y are closer to back curb and the front wheels seem to be slightly in front of the 3. This is a slightly bigger than the 3, similar to X but obviously not as wide and long. Can't wait