Trim size

Trim size is the final width and height of a printed book after the pages are cut, written width first: a 6" × 9" book is 6 inches wide and 9 inches tall. Print-on-demand services such as KDP offer a fixed list of standard trim sizes, and you choose one when you set up a paperback or hardcover.

Common choices include:

• 5" × 8", 5.25" × 8" and 5.5" × 8.5" for novels and memoirs
• 6" × 9" for nonfiction and many novels
• 7" × 10" and 8.5" × 11" for workbooks, textbooks and journals
• 8.5" × 8.5" and 8" × 10" for picture books

Why it matters for indie authors

Trim size drives several other decisions:

• Page count. The same manuscript runs to more pages at 5" × 8" than at 6" × 9".
• Printing cost. Print-on-demand printing is priced largely by page count, so trim size changes your cost per copy and your royalty.
• Spine and cover. Spine width depends on page count and paper, and the cover file has to match the trim size exactly.
• Reader expectations. A book that’s an unusual size for its genre can look out of place next to similar titles.
• Distribution. Not every size works with every channel. On KDP, some trim sizes aren’t eligible for Expanded Distribution.

Example

An author with an 80,000-word fantasy novel compares 5.5" × 8.5" with 6" × 9". At the smaller size the book has more pages, a thicker spine and a higher printing cost. At 6" × 9" it’s slimmer and cheaper to print. She looks at the paperbacks of books similar to hers, chooses 5.5" × 8.5" and formats the interior at that size before her cover designer starts the full wrap.

In AIBookWriter, a novel or nonfiction book gets its trim size in the Format & export step (visual books choose it at the start); the print-ready PDF is laid out at that size, and the spine width for the paperback cover is calculated for you.

Common mistakes

• Formatting before choosing. Changing the trim size later means reflowing the whole interior and redoing the cover.
• Changing size after publishing. KDP doesn’t let you change a published paperback’s trim size in place; you would publish a new edition with a new ISBN.
• A mismatched cover. A cover built for 6" × 9" won’t fit a 5.5" × 8.5" book.
• Ignoring channel limits. Check that your size works with the ink, paper and distribution options you want before you commit.