In David Gerrold's The Trouble with Tribbles: The Story Behind Star Trek's Most Popular Episode, he describes how he used a 12-pitch Selectric to type the 1967 episode. When the studio retyped it in pica (10-pitch) it came out to 90 pages and had to be cut down significantly to fit the show's running time.

The difference amounts to approximately 3 words per page and about 50 words per page.