What trim size should your book be? The honest genre guide

By Tracy Atkins, founder of BookDesigner.ai and BookDesignTemplates.com · 15+ years of print files, 70,000+ authors · Updated July 11, 2026

Why trim size matters more than it looks

Trim size is the finished width and height of your printed book. It is one of the first decisions you make and one of the hardest to undo, because it touches everything downstream. The trim sets how many words fit on a page, which sets your total page count, which sets your spine width, which sets the entire cover wrap. Change the trim after the fact and you are not adjusting a setting, you are rebuilding the interior and the cover from scratch.

So it pays to choose deliberately. The good news is that most of the decision is already made for you by convention. Readers have quiet expectations about what a novel, a business book, or a workbook should feel like in the hand, and matching those expectations makes a self-published book read as professional rather than homemade.

The safe default: 6x9

If you take nothing else from this guide, take this: 6x9 is the workhorse trim of US publishing. It suits nearly all fiction and the large majority of non-fiction, it is stocked by KDP, IngramSpark, and Lulu alike, and it sits comfortably on a shelf next to traditionally published titles. When a book is straight text and the genre does not push you somewhere specific, 6x9 is the choice you will never have to defend.

The reason it is so common is that it balances page count and presence. It is large enough to keep the page count reasonable, so your book is not needlessly thick or expensive to print, and small enough to still feel like a book you would carry.

The common trims, by what they are for

Beyond 6x9, a handful of trims cover almost everything authors publish:

• 5x8 and 5.5x8.5 are the compact, intimate sizes. They are common for shorter fiction, novellas, poetry, and memoir, where a smaller book in the hand suits the reading experience. Trade paperbacks you pick up in a bookstore commonly fall somewhere between 5x8 and 6x9.
• 5.25x8 sits between the two above and is another conventional fiction choice.
• 7x10 and 8.5x11 are the large formats for books that need room: workbooks, manuals, technical guides, cookbooks with layout, and large-print editions built for accessibility. The extra page real estate lets you set exercises, diagrams, and generously spaced text.
• 8.5x8.5, a square trim, serves particular formats where a square page is the point of the design.

A genre-by-genre starting point

Treat this as a starting point, not a rule. Any of the fiction trims can work for any novel; the table reflects what readers most often see.

The cost twist nobody mentions

Here is the counterintuitive part. It is tempting to think a smaller book is a cheaper book. In print-on-demand, the opposite is often true. Cost is driven mainly by page count, and a smaller trim fits fewer words on each page, so the same manuscript runs to more pages at a smaller trim. More pages means a thicker spine and a higher print cost per copy, and a heavier book to ship.

The difference is meaningful. The same manuscript set at 5x8 versus 6x9 can differ substantially in page count, often on the order of 15 to 25 percent more pages at the smaller trim, depending on your type size and spacing. So a choice that feels like it should save money can quietly add pages, thicken the book, and raise the unit cost. If your manuscript is long, moving up to 6x9 can actually produce a slimmer, cheaper, better-proportioned book than squeezing it into 5x8.

How to actually decide

Work in this order. First, let the genre point you at a range from the table above. Second, if the book is long, lean toward the larger end of that range to keep the page count and print cost sensible. Third, confirm your chosen trim is offered by the printers you plan to use; the common sizes here are carried by KDP, IngramSpark, and Lulu, so you rarely hit a wall. Fourth, lock the trim in before anyone builds the interior or the cover, because both are calculated from it.

Once the trim is set, the page count follows from the actual typesetting, and the spine and cover wrap follow from the page count. Get the order right and every number downstream is computed once and stays correct. Get it wrong and you are reflowing the whole book to fix a decision that should have taken five minutes at the start.

Related: Book spine width, the real formulas · Formatting a book in Word · What it really costs to self-publish · All guides