Fiction Lengths and Examples
Version 1.2 (18 August 2011)

Tolstoy Novel: 500,000+ words and up. (Atlas Shrugged is 645,000 and War and Peace is 560,000)

Michener Novel: 290,000 words and up. (Space by James Michener)

Full Length Novel: 100,000 to 120,000 words. (Rogue Clone Series)

Near Full-Length Novel: 80,000 to 90,000 words. (Stark's War Series)

Children's Novel: 50,000~ words per book. (Water Series by Kara Dalkey; 230~ pages in large type; roughly 5” x 7.5” paperback.)

Mid-Length Novel: 50,000 to 60,000 words.

Novella (SFWA): 17,500 to 40,000 words. (Animal Farm has 30,000~ words)

Novelette (SFWA): 7,500 to 17,500 words.

Short Story (SFWA): Under 7,500 words.

Some examples of Short Story lengths:

John Harper Wilson by Allen Steele (5,817 words)
Snowball by Alastair Mayer (5,596 words)
A Monument More Lasting Than Brass by Steven Mohan, Jr. (4,370 words)

It seems to me that 5,000 words is a good length. It's long enough to let you play with the “tools” of the story to give the reader an enjoyable experience. It also comes out as about 25~ pages in mass market paperback format, which makes it attractive to anthology editors in that they have room for other stories to sell the anthology.

Fonts and Formatting

It seems that the most popular font used in mass-market paperbacks is something called Times Ten LT. There is also a rule of thumb that says that you should have a mix between 40 and 60 characters per line in a paperback. Font sizes that achieve this are generally between 9 and 13 points. Margins in mass market paperbacks also seem to be 0.5” from all edges.