In one keyword How many maximum characters can have?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Dave Elliott: Antidisestablishmenterianism. I think that is the longest word in the english language (excluding chemical names) and that comes up as a google serp, so umm you wont find a word too long! 
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  Federico Sasso: 189,819 chars (in English, chemical)
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  Dave Elliott: oooh there is a limit! 
  
  Lopado­temacho­selacho­galeo­kranio­leipsano­dri m­hypo­trimmato­silphio­parao­melito­katakechy­meno­kichl­epi­kossypho­phatto­ perister­alektryon­opte­kephallio­k igklo­peleio­lagoio­siraio­baphe­tragano­pterygon
  
  returns a this word is too long, in google.
  
  pseudopseudohypoparathyroidism does work though!