How Do I Choose the Right Book Size?

What trim size means

Trim size refers to the finished, cut dimensions of a printed book’s pages, expressed as width by height. It is distinct from the manuscript page or the file dimensions used while writing; it is the physical size the reader holds. Once chosen, trim size affects margins, font size choices, page count and how the cover needs to be laid out to wrap correctly around the spine.

Fiction

Trade fiction, particularly novels, commonly uses a small to mid-sized trim, which readers tend to associate with the genre and which keeps a longer manuscript from becoming an unwieldy, overly thick paperback. Genre norms vary, and looking at recently published comparable titles is a useful, low-risk way to sense-check a choice before committing.

Memoir

Memoir often follows similar trim conventions to general fiction and narrative non-fiction, since it is typically a text-driven, page-turning read rather than a reference document. Where a memoir includes photographs, size decisions may need to account for how those images will be reproduced.

Non-fiction

General non-fiction is often produced at a slightly larger trim than genre fiction, partly because readers expect a slightly more substantial physical object for reference-style reading, and partly to accommodate headings, subheadings and any diagrams or charts more comfortably.

Business

Business books frequently use a similar or slightly larger trim to general non-fiction, particularly where the book includes frameworks, bullet-heavy sections or the kind of visual breathing room that supports skimming and reference use rather than linear reading start to finish.

Children’s picture books

Picture books are usually produced at a larger, often square-leaning trim size, because the illustrations are central to the reading experience and need enough physical space to work. Size decisions for picture books generally need to be made very early, often before final illustration work begins, since illustrations are typically composed for a specific page size.

Workbooks

Workbooks, journals and other titles readers write in usually benefit from a larger trim size that gives enough room to write comfortably on the page, along with margins generous enough to allow for binding without cramping usable space.

Poetry

Poetry collections often use a smaller trim size than standard fiction, partly by convention and partly because a smaller page can suit the shorter line lengths and white space that matter to how a poem is read on the page.

Illustrated books

Beyond picture books, any heavily illustrated title, such as an art book, cookbook or graphic memoir, needs trim size decided in close coordination with how the images are composed, since a size chosen after illustrations are finished can force awkward cropping or resizing.

Page count

Trim size and word count together determine roughly how many pages a book will run to. A very small trim size applied to a long manuscript can produce an unusually thick book, while a large trim size applied to a short manuscript can produce a book so thin it looks insubstantial on a shelf. Rough page count estimates are worth calculating before finalising trim.

Spine

Spine width is a direct function of page count and paper type, and it needs to be calculated accurately before finalising a print-ready cover file, since the spine text and any spine artwork depend on knowing the exact width in advance. Getting this wrong late in the process is a common and frustrating source of rework.

Font size

Font size and trim size need to be considered together: a small trim size with a larger, more readable font will produce more pages than the same text set smaller, which again feeds back into spine width and print cost. Readability should generally take priority over squeezing a manuscript into fewer pages.

Margins

Margins need to allow for the "gutter", the inner margin lost slightly to the binding, particularly in perfect-bound paperbacks, so that text near the spine remains comfortably readable and is not swallowed by the binding.

Print cost

Print-on-demand cost is generally driven by page count, and page count is driven partly by trim size and font choices. A larger trim size that reduces page count is not automatically cheaper overall, because per-unit cost calculations from printing platforms vary; checking current cost calculators for your specific book’s planned size and page count is the only reliable way to know actual cost.

Portability

Smaller trim sizes are generally more portable and pocket-friendly, which matters for genres bought largely for on-the-go reading. Larger trim sizes suit books more likely to be read at a desk or table, such as reference-style non-fiction or workbooks.

Platform-supported sizes

Printing platforms only offer a defined list of trim sizes, and this list is set and periodically updated by each platform rather than being open to arbitrary dimensions. At the time of writing, it is not safe to assume a specific dimension is available; the only reliable approach is to check current supported sizes directly.

KDP

Amazon KDP publishes its own current list of supported trim sizes for paperback and hardcover within its documentation. Check the current list on Amazon KDP’s help pages before finalising a design, since available sizes can change.

IngramSpark

IngramSpark similarly publishes its own current supported trim sizes, which may not be identical to Amazon KDP’s list. Authors planning to distribute the same title through both routes should check both platforms’ current documentation and, where possible, choose a size supported by both to simplify production.

Designing before choosing trim

Committing to interior layout, illustration composition or detailed formatting before confirming trim size against actual platform-supported dimensions is a common cause of rework. Confirming size early, against current platform documentation, protects the rest of the production timeline.

Common mistakes

• Choosing a size because a favourite book uses it. A size that suited someone else’s word count, genre and illustration needs will not automatically suit yours.
• Finalising illustrations before confirming trim size. This is a particular risk for picture books and illustrated non-fiction, where resizing images after the fact can be costly and time-consuming.
• Ignoring the effect of trim size on spine width. A cover file built before page count and spine width are confirmed often needs redoing.
• Assuming any dimension can be printed. Printing platforms support a defined list of trim sizes; a size outside that list simply is not an option, at the time of writing.
• Optimising only for lowest print cost. Choosing the cheapest available size without regard to readability or genre norms can produce a book that reads and feels wrong for its category.

Frequently asked questions