Book trim sizes: how to choose the right size for your paperback

Trim size is the final dimension of the printed book after cutting. It affects how the book feels, how many pages it has, its spine width and what it costs to print — so choose it before you format the interior or commission a cover.

The most common US sizes are 5 x 8, 5.25 x 8, 5.5 x 8.5 and 6 x 9 inches. 6 x 9 is the default for non-fiction and many novels. 5.5 x 8.5 and 5 x 8 feel more like a traditional trade paperback for fiction. 5.06 x 7.81 is a common choice for genre fiction that wants a mass-market feel.

Larger formats such as 7 x 10 and 8.5 x 11 suit workbooks, textbooks, cookbooks and low-content books like journals, where the page needs room for exercises or images.

Genre convention matters more than personal taste. Pull five bestselling paperbacks from your category and measure them. Readers notice a novel that looks like a workbook.

Trim interacts with word count. The same 80,000-word novel may print at around 300 pages at 6 x 9 and noticeably more at 5 x 8. More pages mean a higher print cost per copy, which reduces royalty at the same list price.

KDP supports a wide range of standard trims for paperbacks and a narrower set for hardcovers. Check that your chosen trim is available for every format you plan, and that its paper and color options match your needs.

Once chosen, set your document's page size to the trim exactly, then set margins and gutter for your final page count. Changing trim later means reformatting the interior and regenerating the cover.

Manucheck checks that your print PDF's page size matches the trim you selected and that your cover wrap is calculated for that trim and page count.