Board Thread:Lore Discussion/@comment-176.205.177.128-20170208120213/@comment-1600847-20170208125657

Daggerfalls Illiac Bay region was 161,600 square km (100,413 mi), and that's only about 1/4 to 1/5 of High Rock, whereas Skyrims map of the entire province is 37 square km (14 mi).

So we don't know how big each province is, it's never said in game so all we can do is speculate.