According to this article it would take you over an hour to run from one side of Cyrodiil to the other...
http://www.gameranx.com/updates/id/16676/article/the-size-of-the-elder-scrolls-online-s-world-calculated/
And then there is a lot more math... parsonally i think their are so many unstable variables that they must be way of, but even then its larger then any other handcreated MMo at release....
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The math is indeed all wrong...
the whole math is flawed... a character moves about 400 meter/ minute, thats about 8 minutes over 3 km..
assuming the world is 3 x 3 zones square, it would take you about 24 minutes to cross Cyrodiill
with each of the PvE alliances being roughly 3/4 of cyrodiil, means taking a little more then 20 minutes to cross a whole alliance from one side to another...
Meaning that all 3 PvE alliances together are about as big as Kalimdor in WoW, which means that the world will be a little smaller then WoW at release... Nothing to really brag about if you ask me,,.. But then there might be many many many open world dungeons...