How many King Louis has France had?

Answer 1

18 if you count the son of Marie Antoinette and her husband Louis XVI--this boy died during the Revolution. He would be Louis XVII and then his uncle became king after a Revolution and he reigned as Louis XVIII.
Depends on whether you're a raging monarchist or not. Louis XVIII was the last of the 'legitimate' line, but Louis XVII never actually ruled; so you could say 17 or 18 according to taste. If you're an Orleanist, you might add Louis-Philippe, making 19 in all.