Writers worry quite a bit about how long their books should be. And people like me worry quite a bit about how to give the right advice - because you want a straight answer, but the only true answers are quite wiggly.
As a writer in the arty sense, the truest answer I can give, though it's not the one you want, is that "the book should be the right length for the story." The story should fit beautifully inside the covers (whatever size those covers are) and the reader should not feel that you either spun it out or cut it short in its prime with a headlong rush towards the end.
As a writer in a practical frame of mind, however, I have to have some commercial considerations in mind. These considerations are even truer for the unpublished author, who has not established an audience.
The first thing I'd say is that if you're going to look around to check out the lengths of similar books to yours, a) that's a very good idea indeed, and I hope you do, BUT b) do not consider the unusually short or long in this equation; and do not consider any books which had phenomenal success despite being extremely short or long. For example, if you're looking at the lengths of books for 10-12 year-olds, ignore the length of the Harry Potter books. Extremes and exceptions tell you nothing useful.
The second thing I'd say is that word count is a bit of a red herring. Yes, we have to use it because it's the only objective method we have, and agents and publishers need it. But publishers are perfectly capable of making a book look longer or shorter than it is - by judicious use of font size, font type and letter/line spacing. That's what they'll do, but unfortunately it doesn't help you because they do sometimes get quite hung up on word length at the acquisition stage.
- Each book will be costed at an early stage in the process - often at the acquisitions meeting which is also deciding whether to accept it. The cost must account for the number of pages to be printed. The price points of particular books don't vary as much as word length, and they have to compete price-wise: so the price cannot usually reflect the different costs of production between a book of, say, 300 pages and a book of 500 pages. Therefore, an over-long book which a publisher is unsure about is more likely to be rejected than if it was a standard length.
- Readers do sometimes consider the value of a book according to how long the pleasure will last. So, some readers will reject a book if it's too short, especially by an unknown author. I know that doesn't seem right, as a book's value is not related to length, but it's what many readers do, often subconsciously.
- Similarly, and particularly in some genres, a book that's too long may put readers off. This is particularly the case in children's writing.
- Identify twelve books which you think would be your competitors - with the same readership. But do not include extremes (see above).
- Remove what look like the two shortest and the two longest.
- Do a rough word count for each of the remaining eight: simply do an accurate word count for ten full pages in each and multiply by the number of pages. Make some vague adjustment for pages which only have a few lines on them.
- Is there a very large range? For example, is the shortest 90,000 and the longest 250,000? In that case, your genre is wide open and you don't have too much to worry about as long as you keep within that range. If they all seem a similar length, work out the average and try to stick to within 15-20% of that average.
As an enormous generalisation, because I sense that you want me to give figures, I'd suggest that a starting-point is that a novel for adults will generally be longer 100,000 words and a novel for teenagers will be less than that. My novels have ranged from around 42,000 (Mondays are Red) to 78,000 (the Highwayman books). When you hold them in your hand - which is what really matters to the reader, who has no idea of the number of words - Mondays are Red feels too short to me and the Highwayman books feel too long, especially since they are aimed at younger teenagers, including 10+. Despite that, they both did well, but I'll never know who was put off by the length of the Highwayman books.
In my opinion as the author and a keen book buyer, my new baby, Wasted, feels like the perfect length. Mmmm, beautiful - I'm still at the stroking stage, I warn you. It feels chunky enough to last a good number of hours, but not at all off-putting. It has 352 pages and contains something not much over 60,000 words. That's the target I've given myself for the next one, and it just "feels right".
Wasted blog. All you have to do is register as a follower and you'll be entered each week. The Wasted blog is launched on April 23rd and from that day on I offer you a feast of info, snippets, competitions, stories of fate / luck / chance, and lots of ways for you to get involved. Head over there now so that you are with us when we begin the fun and games!