Morrowind = @ 10 square miles
Awhile back I did a test for Morrowind similar to the one for Oblivion I mentioned above. I opened the construction set and counted the number of cells I found as I moved laterally through the line of cells that pass through Balmora. I counted 26 cells. Traveling from the tip of the Ebonheart peninsula up to the last island above Vas I counted 40 cells.
The Construction Set help file tells us that "Each exterior cell is 8192 units by 8192 units or 385 feet by 385 feet." 385 x 26 is 10,010. One mile is 5, 280 feet long so that means that Vvardenfell is approximately 2 miles wide, according to the CS. 386 x 40 is 15, 400 feet, which comes to approximately 3 miles. So if the construction set help file is correct, the size of Vvardenfell is approximately 6 square miles.
In my opinion there are three main reasons why Vvardenfell
feels larger than Cyrodiil:
1. Fog. Being able to see White Gold Tower from practically every square inch of Cyrodiil makes the game world look and feel as small as a model train layout in some kid's basemant.
2. Running speed. Running speed was increased in Oblivion, reducing the real-world time it takes to get from one end of the game world to the other.
3. Starting position. Oblivion places the player near the center of its game world. Morrowind places the player in a corner of its world. All Vvardenfell is in front of the Morrowind player at the beginning of a game - it is a long (and harrowing) journey to reach the northern coastline. It is not nearly as long a journey to reach a border of Cyrodiil.
4. Invisible barriers. The sea around Vvardenfell went on forever. Cyrodiil is surrounded by invisible walls. To make matters worse Oblivion announces that fact with repeated "You cannot go that way. Turn back," messages whenever the player goes too far in any direction. I believe that, psychologically, this makes the game world feel very finite, whereas Morrowind's infinitely-generating cells made that game world feel infinite.