The word length for a manuscript is not set in stone, but here are some general guidelines that are well worth bearing in mind as you write, and of course later as you submit.
Think of a paperback that you own which is between 300 and 400 pages: this is the typical paperback novel and it's almost certainly 80,000 to 100,000 words long.
But, here are some of the common variations you might encounter:
- a literary novel can often weigh in as shorter, say 60,000 to 80,000 words
- a 'blockbuster' can be longer, as can a sci-fi or historical fiction novel. (Crime tends to stay within the typical length.)
- a children's book is normally shorter and a picture book (being mainly illustration based) can be as little as 100 words
- a children's novel for 5- to 8-year-olds is likely to be around 20,000 words
- Once you are writing for the 8- to 12-year market, I would aim for around 40,000 words. (Teen or cross-over fiction comes in at adult fiction lengths.)
Why does amy of this matter? And surely if you have written a masterpiece, the publisher should accept the length as it is? Well maybe. Publishers are driven in equal measures by commercial and creative impulses. They will still consider the odd anomaly - but you are then having to persuade them that much more that your work is worth taking on.
Why make it harder for yourself? Working within a length framework gives you structure, and also a guide as to how much time you have to develop a plot, and introduce characters.