Choosing a trim size
Trim size is the width and height of a finished page — 6 x 9 inches, say, measured after the printer has cut the block square. It sounds like a detail to settle later. It is actually the first structural decision in the book.
Change the trim and the text re-flows, the page count moves, the spine gets thicker or thinner, the cover changes proportion, and the cost of printing every copy changes with it. Choose once, early, and you never think about it again.
The conventional sizes and what they signal
Trim sizes are a language, the same way cover conventions are. A reader has handled a few hundred books and knows, without ever putting it into words, what shape a thriller is.
- 5 x 8 and 5.25 x 8 — small-format fiction. Literary novels, story collections, poetry, novellas. Intimate in the hand, modest on a shelf. A 400-page business book at 5 x 8 looks like it is trying to be a different book.
- 5.5 x 8.5 — the digest size, and the most common self-published novel. Also standard for shorter nonfiction: how-to, self-help, a memoir under about 70,000 words. It reads as a real trade book without the bulk of a 6 x 9.
- 6 x 9 — the default, and the one to pick if you are unsure. Trade nonfiction, memoir, history, business, and most genre fiction live here. It is also what most print-on-demand books are, which means it is the shape of the last three print books your reader bought.
- Larger formats — 7 x 10, 8 x 10, 8.5 x 11 and up, for workbooks, textbooks, cookbooks, art and photography books. Anything with exercises to fill in, wide tables, code listings or full-page images needs the width. A novel at 8.5 x 11 reads as a manual.
The trade-off nobody mentions
Here is the part that surprises people: the smaller book is usually the more expensive book to print.
The words don't change. The page that holds them does. Drop from 6 x 9 to 5 x 8 and each page carries noticeably fewer words, so the same manuscript needs more pages — commonly 20 to 30 percent more. More pages means more paper, a thicker spine, and a higher print cost on every copy you will ever sell.
Run it the other way and it inverts. A larger trim fits more words per page, the page count falls, the spine gets thinner, and the unit cost drops with it. For most manuscripts, 6 x 9 is the cheaper book to make — and the more shelf-conventional one.
That is worth knowing before you pick 5 x 8 because you like how it feels in the hand. Liking it is a legitimate reason. Just choose it knowing what it adds per copy, and knowing the book will be thicker than you pictured it.
In the Cover Maker. Set the trim, the printer and your real page count and the spine and full wrap are measured for you, so you can put 5.5 x 8.5 next to 6 x 9 and see both covers at their true proportions before you commit to either. Start a book → · about the Cover Maker
Why it is a decision to make once
Changing trim later is not a setting you flip. The interior re-flows from page one: line lengths change, paragraphs break differently, chapter openings land on new pages, and the total page count moves.
Page count drives spine width, so the cover is now wrong too — the wrap is a different size and the spine text no longer fits the space it was set for. If you have already proofed an interior, changing trim means proofing it again from the beginning.
So decide before you typeset, not after. The Interior Formatter builds every page from the trim you give it, and margins scale with the trim, so the choice has to be made going in.
Genre expectation beats personal taste
The common mistake is picking the shape you personally like. Readers don't experience trim size as taste — they read it as a category signal, and a book that is the wrong shape for its shelf looks wrong even when everything about it is well made.
An oversized page on a novel, a narrow page on a business book, an art-book format on a thriller: each one tells the reader, before a single word is read, that this came from somewhere other than a publisher.
The check is the same one that works for covers. Find five direct comparisons — same shelf, same reader, published recently — and look at the printed dimensions in their listings. If four of the five are 6 x 9, that is your answer, and preferring 5 x 8 is not a good enough reason to overrule it. See What makes a cover sell for the same argument applied to the front.
What this site supports
Four trim sizes work on every printer here — 5 x 8, 5.25 x 8, 5.5 x 8.5 and 6 x 9 — across Amazon KDP, IngramSpark, Lulu and B&N Press, and across all three bindings: perfect bound paperback, case laminate hardcover, and dust jacket.
Choosing inside that set means the same book can be printed anywhere you later decide to sell it, with no re-design and no re-flow. That is also the practical case for staying conventional: a trim size only one printer offers is a trim size that ties your book to one printer.
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 in this guide: Where to print · Book cover dimensions · Spine width