Book trim sizes explained: which size should you choose?

"Trim size" is just the final, trimmed dimensions of your printed book — width × height, given in inches. It's one of the first decisions you'll make, because it shapes how your book feels in the hand, how many pages it runs to, and what it costs to print. The good news: there are only a handful of sizes that actually matter, and almost every genre has a conventional choice.

The common sizes, at a glance

Trim size	Best for
5 × 8 in	Novels, novellas, poetry — compact and "literary"
5.25 × 8 in	Fiction wanting a touch more room than 5×8
5.5 × 8.5 in	The all-rounder — fiction, memoir, general nonfiction
6 × 9 in	The default for paperbacks — nonfiction, business, longer novels
4.25 × 6.87 in	Mass-market paperback (the rack-sized airport novel)
A5 (148 × 210 mm)	The European standard for fiction and nonfiction
7 × 10 in	Workbooks, manuals, textbooks, cookbooks
8.5 × 11 in	Large workbooks, journals, illustrated nonfiction
8 × 8 in	Square — children's books, photo and gift books

How to pick

Start with your genre's convention — readers subconsciously expect it, and bookshops shelve by it. For most fiction, 5×8 or 5.5×8.5 looks and feels right. For nonfiction, business and self-help, 6×9 is the safe default. Poetry usually wants something slim like 5×8 or 5.5×8.5 so lines don't wrap. Workbooks, cookbooks and anything with tables or images benefit from the extra width of 7×10. Children's picture books are typically square (8×8) or landscape.

The simplest test: find three published books you admire in your genre, measure them, and copy the most common size. You almost can't go wrong.

Trim size affects page count — and cost

A smaller trim fits fewer words per page, so the same manuscript runs to more pages; a larger trim runs to fewer. Page count matters because print-on-demand services charge per page, and because very thin or very thick books have minimums and maximums. As a rough rule, moving a typical novel from 6×9 down to 5×8 can add 15–25% more pages. If your book is borderline too thin (under ~24 pages won't print) or too thick, nudging the trim size up or down is the easiest lever.

Will KDP and IngramSpark print it?

All the sizes above are supported by Amazon KDP and IngramSpark, the two services most indie authors use. KDP lists 6×9, 5×8, 5.5×8.5 and others as standard; IngramSpark supports an even wider range. Stick to a standard size and you'll have no trouble — and you'll usually get the cheapest print cost and widest distribution.

Setting it in Bookmint

In Bookmint, open the Design tab → Page size and pick from the same standard trims — 6×9, 5×8, 5.25×8, 5.5×8.5, mass-market, A5, 7×10, letter and square. The live preview re-flows at the true trim size instantly, so you can try a couple and see which feels right before you commit. When you export, the print-ready PDF is built at that exact size with the correct margins baked in, and the pre-flight check warns you if your binding gutter is too small for the page count.