What is a trim size?

A book's trim size is the size of its pages once the printer has cut them — the dimensions of the finished book, width first. It is one of the first decisions to make for a print edition, because the interior layout, page count, spine width, cover size and printing cost all depend on it.

Common trim sizes have genre conventions. In the US, 6" × 9" is the most common size for trade paperbacks, especially nonfiction; 5" × 8", 5.25" × 8" and 5.5" × 8.5" are popular for novels; 8.5" × 8.5" and 8.5" × 11" suit children's picture books, workbooks and cookbooks. In India, the UK and much of the world, A5 (148 × 210 mm) is a familiar size. Browsing the shelf in your genre is the quickest way to pick something readers will find normal.

Not every printer offers every size. Each print-on-demand service publishes a list of standard trims, and some sizes cost more to print or are not eligible for every distribution channel. Check the platform's current trim size list before formatting your interior.

Changing trim size later is expensive in effort: a smaller trim fits fewer words per page, so the page count rises, the spine gets wider and the cover has to be rebuilt. Settle it before you design either.