Sf vs speculative fiction

Sf

noun
  • a book size one sixty-fourth of the size of a standard uncut sheet of paper (less 7.5 cm (3") in height) 

speculative fiction

noun
  • A particular work belonging to this class. 

  • A class of fiction involving fantastic, supernatural or futuristic elements, including fantasy, horror, and science fiction, dealing with worlds, themes, and characters not part of everyday life. 

How often have the words Sf and speculative fiction occurred in a corpus of books? (source: Google Ngram Viewer )