We got into that on the forum last year, the scale of the changes were pretty egregious, before the changes the Sword Coast region alone is about the size of Europe, but in 3E everything is cramped and on top of each other.
For just the Sword Coast region, leaving off the rest of Faerun:
In the 3E/4E material the Sword Coast region as defined in SCAG is ~2.2 million square miles (or ~5.7 million square kilometers approximately twice as large as India)
In the 1E/2E/5E material, the Sword Coast region is over 5 million square miles (or nearly 13 milliom square kilometers, just shy of Antarctica, the only country on Earth bigger than the Sword Coast region is Russia).
That means the land that disappears and comes back is about the size of Australia. Just for the Sword Coast.
The article is here: