How many French kings were named ‘Louis’?

There were 18 French Kings named Louis, beginning with the Carolingian Empire with King Louis I, the Debonaire from 814-840. The last King Louie was King Louis-Phillipe in Orleans from 1830-1848.

http://historyscoper.com/frenchkings.html

King Louis 16th was the last one. He was guillotined in 1793 after the French revolution.

https://en.wikipedia.org/wiki/Louis_XVI

Depending on the definition of "king" before, during and after the revolution, it could be:

16 up to the start of the revolution (1789).
17 if you include Louis XVII's short reign after his father Louis XVI was executed.
18 if you also include Louis XVIII who ruled briefly after Napoleon's defeat until Napoleon's return.
19 if you also include Louis XIX who never actually ruled and abdicated in 1830.
20 if you include Louis-Phillipe, Duke of Orleans, who was the last king up to the 1848 revolution.

Most sources say 17 or 18 King Louis.
http://europeanhistory.about.com/od/france/fl/The-Rulers-of-France-From-840-Until-2015.htm

Here is the list of the French kings called Louis, although it is disputed if all of them were actually "kings". But they numbered 19 altogether. Louis XIX reigned for 20 minutes, which is probably a world record.

Louis the Pious, Emperor and King of the Franks from 814 to his death
Louis the Stammerer, the eldest son of Charles the Bald and Ermentrude of Orléans
Louis III of France, king of Western Francia
Louis IV of France, king of France from 936 to 954
Louis V of France, son of the Frankish King Lothair and his wife Emma
Louis VI of France, King of France from 1108 to 1137
Louis VII of France, King of France from 1137 to 1180
Louis VIII of France, King of France from 1223 to 1226
Louis IX of France, King of France from 1226 to 1270
Louis X of France, King of France from 1314 to 1316
Louis XI of France, King of France from 1461 to 1483
Louis XII of France, King of France from 1498 to 1515
Louis XIII of France, King of France and Navarre from 1610 to 1643
Louis XIV of France, King of France and Navarre from 1643 to 1715
Louis XV of France, King of France and Navarre from 1715 to 1774
Louis XVI of France, King of France and Navarre from 1774 until 1791
Louis XVII of France, the son of King Louis XVI of France and Marie Antoinette
Louis XVIII of France, King of France and Navarre from 1815 to 1824
Louis XIX of France, King of France and Navarre for twenty minutes in 1830 before his abdication

https://en.wikipedia.org/wiki/Louis_(given_name)#Kings_of_France