It's not as simple as that...besides, the rankings now change every month.
new to chess...question on fide rankings
Usually, the top ranked played does eventually become the WCC, but they should dethrone the reigning champion in the process. Without it, there are legitimacy issues with the title. Karpov had to work long and hard to "prove" himself the WCC, just because Fischer refused to play.
i always wondered do fide rankings really mean the best of the best.... do elo points determine who is really the best chess player in the world
so looking at the current rankings....
is carlsen the best player in the world, because he is ranked number 1
karjakin is ranked 5th does that make him the 5th best player
caruana is ranked 8th... does that make him the 8th best player in the world and so on?