If we talking about markets. Its countries. And USA, Japan and Germany are surely bigger than Korea.
If we talk about music branches. Pop, HipHop, latin and maybe edm are bigger than Kpop.
But i think Kpop is allready bigger than Rock or country music.
The last statistics i saw were that Korea is the 6th largest music market in the world and that Kpop is the seventh most popular genre in the world.