The average book length

An average English language literary novel would have around 80-100,000 words (depending on genre) and 5,000-7,000 sentences. An average trade 5.5x8.5 inch book may have approximately 300 words per page and a 6x9 inch size book may have 350 words per page. The smaller, cheaper mass market paperbacks (usually 4.125 x 6.75 inches) pack on average 250 words per printed page but longer books may pack more than 350 words per printed page.

The median length for all Amazon books is about 64,000 words.  Here are some stats about book lengths taken from Amazon's text stats taken a couple of years ago.

Pride and Prejudice
Words: 120,528 (29% have more)
Sentences: 5,878 (35% have more)
Words per Sentence: 20.5 (42% have more)

Effi Briest (German)
Words: 98,455
Sentences: 5,501
Words per Sentence: 17.9

Anna Karenina (translated)
Words: 334,108 1% have more
Sentences: 19,345 2% have more
Words per Sentence: 17.3

James Clavell's Shogun
Words: 428,978
Sentences: 43,647
Words per Sentence: 9.8

Animal Farm
29,966 words (75% of books have more words)

Ethan Frome
30,191 words (75% of books have more words)

The Crying of Lot 49
46,573 words (64% of books have more words)

Slaughterhouse-Five
47,192 words (64% of books have more words)

Lord of the Flies
62,481 words (51% of books have more words)

Brave New World
64,531 words (50% of books have more words)

The Adventures of Tom Sawyer
70,570 words (45% of books have more words)

Portnoy’s Complaint
78,535 words (41% of books have more words)

Lolita
112,473 words (21% of books have more words)

Madame Bovary
117,963 words (18% of books have more words)

Mansfield Park
159, 344 words (9% of books have more words)

Moby-Dick
209,117 words (4% of books have more words)

Ulysses
262,869 words (2% of books have more words)

Middlemarch
310,593 words (2% of books have more words)

War and Peace
544,406 words (0% of books have more words)