This is difficult to answer without first defining what to count. Using James Gifford’s Opus list in his Robert A. Heinlein Reader’s Guide I (Heinlein Society President Ken Walters) counted 205 listings. These included everything: essays, articles, forwards, afterwards, acknowledgments, book reviews, interviews, speeches, screen plays, scripts, etc.

In Heinlein Journal No. 19 July 2006 Bill Patterson says 63 books which include the short story collections (some of which exist in multiple formats). In the Wikipedia entry for Robert they state: Heinlein published 32 novels, 59 short stories, and 16 collections during his life.