As I understand it the land area is a little smaller than the land area in Oblivion.
The often quoted number is 16 square miles (the equivalent of a square with 4 miles per side). I've seen the number 14.5 square miles for Skyrim. Morrowind is also a bit smaller than Oblivion.
But that number is not quite right I think. I once counted the major cells. It came out to much less than 16 square miles (which doesn't take into account slopes).
Of course that does not count dungeon areas, or any other non map areas.
As I understand it Daggerfall is huge because it's landscapes are computer generated, where as Morrowind, Oblivion and Skyrim are hand crafted.