Being that my world collides with the elemental planes, and is situated atop the lower planes, in what used to be a Cell of the Plane of Dreams it has no real end and no real beginning so it is as large as adventuring requires it to be, and as small as the eye of a needle.
Yes I know that was not what you really wanted to know but its my world...
The area my players are currently in is roughly the size of the United States, and Canada surrounding this area is the Fey Mists, and in the north eastern corner of the area their is the Mistlands, a devastated land that once was the Capital Kingdom of the Worlds elven peoples. When the white son of Darkness opened the Seal of Kirith thus shattering it and freeing Kirith again into the world he destroyed all of the land up to Grenai (300 miles away) and the nature of the land changed (A ring of mountains rose up and sealed the mists of Kirith from the rest of the world)
Some three thousand years later Sorcerers are hunted by Magic Hunters with born talents to kill, and stop magical beings The Elemental lords (or the last of them anyway) are attempting to stop the death of the Hearth (due to magic seaping out of the world) with any means possible. Fenyaronde the Ice lord in the north is slowly driving an Ice age down into the southlands, Whist the World tree has sent the Five from Llyrandwil, and Lord Death is rearing his ugly head and giving battle to the Fire King
Mysteriously the Sea King has fallen silent, and the Wind Lady has faded from the realm. The Nox Arcanum is beginning to loose the battle as magic fails to function. And it is snowing in Nyambra, coating the desert in a white blanket.