The traditional answer to this question is “as long as it needs to be,” but there are still expectations from readers and publishers alike.
When writing a story, the first thing to consider is what you’re writing the story for. Making a web novel? Self-publishing? The exact word count won’t matter much.
But if your goal is to submit your story or book to a publisher for consideration, the first and only place you should look for length requirements is the publisher’s website. There is no universal definition of where a novella ends and a novel begins, and a short story that’s acceptable for one magazine might be too long to be considered for another.
When writing to a word count, don’t try to hit it exactly. Not all programs count words the exact same way, and there’s some ambiguity as to whether chapters, titles, or section headings contribute to word count. Keep a healthy buffer of at least 100 words or so for short stories. For very short fiction, such as microfiction, it’s expected that someone will use the full extent of the count available.
Below is a chart of typical length bands for different types of stories. Take these as guidelines, not hard cutoffs.
Chapters can be any length. Some books have no chapters at all. Some have sprawling chapters with dozens of scenes in each. And some chapters take up less than a page to bring emphasis to a specific moment in the story.
That said, a typical chapter is 1,500 to 5,000 words. Most readers will consider chapters in this length range normal.
Chapters are a useful pacing element, like mile markers for your story. Readers frequently use chapters as stopping points and will pick books back up at the top of the next chapter. Chapters are also a logical point to transition from one place, time, or perspective to another.
Chapters with predictable lengths are a great way to keep the story moving and offer your readers a sense of progression through a longer work. While chapters of varying sizes are rarely a detriment, they cease to communicate anything useful to the reader about their place in the text. They may still be useful for transitions or to call attention to significant moments within the text.