Beginning writers often ask, how long should my work be?
Here is a helpful chart for novels I found on the site of another author, Barbara Kyle:
Adult novel: mystery, suspense, thriller, romance, mainstream, and literary:
80,000-90,000 words: The ideal range to aim for.
90,000-100,000 words: A little too long, but may be fine.
70,000-80,000 words: May be too short, but could be okay.
100,000- 110,000 words: Likely too long, but could be okay.
Below 70,000 words: Too short. with the exception of cozy Mystery.
Above 110,000 words: Too long, with the exceptions of Sci-Fi and Fantasy, which are generally longer than other genres.
Middle Grade: 20,000-55,000 words.
Upper Middle Grade: 40,000-55.000 words.
YA: 55,000-80,000 words.
Of course, there are other lengths to tell stories in: short stories, novellas, short novels... in other words, keeping the above in mind, take as long as it needs to be to tell the story well.
If you are writing for presentation to a particular publication, or publisher, there will be guidelines as to what they are willing to accept. In my own novels, I usually aimed for 90,000 to 100,000 words. One manuscript I handed in to a small publisher resulted in the following request: We like it, but while we could publish it as an ebook, it is too long for us to bring out in a print edition. Why don't you cut it in half, flesh out these out, and write a third. So I did, and the Toltec Trilogy was the result.
For my novellas, like the Housetrap Chronicles series, I always start out with a target of 30,000 words in mind, but usually just keep writing until OI come to the end of the story.