Word length is something beginner writers tend to obsess about. It is good to know the basic rules of thumb, but you shouldn’t get too bogged down in the detail.
Here’s the most basic rule of thumb: an adult novel is 80,000-100,000 words.
Different genres do have their different expectations, of course. Romance tends to be shorter; epic fantasy tends to be longer (but not as long as you’d think, for a debut novelist!). But, really, there’s not a lot in it.
Young adult novels tend to be quite a lot shorter, but have a greater range: anything between 45,000 and 80,000 words is probably fine.
Children’s books are of course shorter still.
For more detail, check out the excellent articles at http://www.guidetoliteraryagents.com/blog/Word+Count+For+Novels+And+Childrens+Books+The+Definitive+Post.aspx
Also, below you can see some estimates of word count from various books (I think I used this tool for some of these; others I worked out myself by counting the number of words on one page and extrapolating).
What about shorter fiction? Writer’s Edge have some word counts for these. According to this, a novella should be at least 15,000 words and a short story should be less than 6,000.
Random list of estimated word counts:
- Jim Butcher: Stormfront: 240 w/p; 322pp; 27 ch; c 72000 wds
- Rachel Caine: Cape Storm: 295/p; 303pp; 12 ch; c87000 wds
- Patrick Rothfuss: Name of the Wind: say 450/p; 614pp; 92 ch; c 276,300 wds
- Robert Jordan: Eye of the World: 445/p; 782pp; 53 ch; c 345,000 wds
- Raymond Feist: Magician: 485/p; 687pp; 34 ch; c 328,000 wds
- Terry Goodkind: Sword of Truth 1: 400/p; 774pp; 49 ch; c 309,000 wds
- Terry Brooks: Shannara: 154k; 158k; 164.5k
- Traci Cavanagh: Black Magician trilogy: 119k; 148k
- Ian Irvine, book 1 of Mirror Quartet: 193k
- Garth Nix: Abhorsen trilogy: 52.7k; 133.8k; 99.2k
- Liam Hearn: Tales of the Otori: 86.8k; 103.8k; 90.9k
- John Marsden: Tomorrow when the war began …: all 78k
- J.K.Rowling: Harry Potter: 77k; 85k; 107k; 191k; 257k; 169.5k??
- Philip Pullman: Northern Lights: 116.5k; Subtle Knife: 98.6k
- Susan Cooper: The Dark is Rising: 82k; 40k; 56k; 75k; 86k
- Horrible Histories: 18.5k; 17.8k; 19.8k …
- Animorphs: 23.5k; 26.6k; 30k; 28k
- Lemony Snicket: 33.7k; 24k; 43.7k; 40k; 48.7k
- V.M. Jones: Karazan series: 66k; 61.7k; 67.4k