How long should a book be?
Every author asks this, and gets half an answer. The usual reply is a table of genre ranges, which is true as far as it goes and stops exactly where the interesting part starts.
Word count is two separate things wearing the same number. It is an expectation — readers, agents and retailers have a rough idea of how thick a thriller is — and it is a production fact, because words become pages and pages are a physical object that costs money to print. Most advice covers the first and ignores the second.
The ranges readers expect
These are approximations, not standards. They describe where the bulk of published work sits in each category.
- Picture books. Very short. Often under a thousand words, frequently a few hundred. The pictures carry the story and the page count is fixed by the printing.
- Chapter books and middle grade. Short. Chapter books run to a few thousand words; middle grade novels are usually in the tens of thousands rather than near a hundred thousand.
- Young adult. Moderate. Shorter than adult fiction as a rule, though YA fantasy routinely runs to adult length.
- Adult genre fiction. A broad band. Romance, mystery, crime, thriller and science fiction cluster in a wide middle — comfortably under a hundred thousand words in most cases, and nobody blinks either side of that.
- Epic fantasy and historical fiction. Longer, by convention and by need. Both genres spend words on world and period that a thriller spends on plot.
- Literary fiction. Variable, and the least governed of any category. A short literary novel is a form, not a failure.
- Novellas and short nonfiction. Deliberately short. The brevity is the product — a single argument, a single arc, read in one sitting.
- Business and self-help. Moderate. Long enough to be a book, short enough that the idea does not thin out.
These are conventions, not rules. An excellent book outside its band is still an excellent book. What it loses is easy recognition: a reader scanning a category page reads thickness as a signal about what kind of thing they are holding, and a book that reads as the wrong size has to work harder to be understood before it can be judged. That is a real cost, and it is not the same as a quality problem.
Words become pages, and pages are an object
Here is the half nobody mentions.
Your word count divides by a words-per-page figure to give a page count, and the page count is load-bearing across the whole production. Roughly 250 to 300 words a page is typical for a novel, depending on trim size and type size — so an 80,000-word novel lands somewhere near 270 to 320 pages, and a 150,000-word novel near 500 to 600.
Those are not two versions of the same book. They are different objects.
- Spine width. KDP white paper bulks at 0.002252 in a page. 270 pages is a spine of about 0.61 in; 550 pages is about 1.24 in. Cream is thicker still, at 0.0025 in a page.
- Print cost. Print-on-demand charges by the page. A book twice as long costs meaningfully more to manufacture, every single copy, forever.
- Your price floor. That manufacturing cost sits under your list price, and a long book cannot be priced like a short one and still return anything. Run the real numbers in your printer's own cost calculator before you settle on a price — see Pricing a self-published book.
- Your gutter. The inside margin has to grow as the book thickens, because a thick book does not open flat. Up to 300 pages, 0.5 in of total inside margin is right; 301 to 500 wants 0.625; 501 to 700 wants 0.75. Crossing 300 pages quietly takes width away from your text block.
In the Interior Formatter. It pours your manuscript at a real trim size and gives you the actual page count, then that count flows to the Cover Maker and computes the spine from your printer and paper color — so you can see what a length decision costs before you commit to it. Start a book → · about the Interior Formatter
The levers between words and pages
Words per page is not a constant. Four settings move it, and moving them is legitimate.
Trim size. A larger page holds more words. The same manuscript is visibly fewer pages at 6 × 9 than at 5 × 8. See Choosing a trim size.
Type size and leading. A point of type size or a point of leading, applied across a whole book, moves the page count by tens of pages. See Type size, leading and the line that reads well.
Margins. Wider margins mean a narrower text block and more pages. Narrower margins do the reverse, up to the point the page looks cramped.
Adjusting these to reach a page count is normal production work. It is also obvious when overdone. A novel set at 9 point with thin margins to keep the print cost down reads as cheap on the first page, and a thin book padded out with 14-point type and a huge leading reads as padded. Within reason nobody notices; past it everybody does.
The limits that are hard
At the extremes the printer decides, not you. KDP paperbacks run from 24 to 828 pages, and hardcovers from 75 to 550 — so a 150,000-word novel may simply not be available in hardcover at your chosen trim and type size. KDP also prints spine text only at 80 pages and above, which is why very short books arrive with a blank spine.
Past the ceiling there is one answer: split the book into volumes. That is a real decision with covers, titles, metadata and pricing attached to it, and it is the usual reason a large print edition of a long novel becomes two books.
Make yours
Everything here is built into the tools, and they are free to use: name your book, bring your manuscript or your artwork, and work as long as you like. You only pay when you want the files without the preview watermark.
Next: The style sheet: how a series stays consistent · Also: How to calculate spine width · Margins and gutters · Choosing a trim size