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KDP supports a range of trim sizes. The most common for fiction is 6" × 9" — a standard trade paperback size. Popular non-fiction sizes include 5.5" × 8.5" (slightly smaller, often used for business books) and 7" × 10" (used for workbooks and visual non-fiction). Children's picture books and activity books often use 8.5" × 8.5" or 8.5" × 11". Low content books commonly use 6" × 9" or 8.5" × 11" depending on the interior layout. The 5" × 8" size is sometimes used for novels to make a shorter book appear longer on the shelf.
KDP's printing cost is affected by trim size — larger books cost more to print per page. An 8.5" × 11" book will have a higher per-page printing cost than a 6" × 9" book of the same page count. Trim size also affects your KENP page count for KU books: larger trim sizes with larger text result in fewer normalised KENP pages, which reduces KU income per physical page. Format your book at a trim size standard for your genre to meet reader expectations and keep printing costs reasonable.
Can I change my trim size after publishing?
Yes, but you'll need to reformat your interior file and potentially redesign your cover. Your page count will change when you reformat for a different trim size, which changes your spine width, which means a new cover. It's worth getting your trim size right before you format to avoid doing everything twice.
What trim size should I use for a novel?
The industry standard for adult fiction trade paperbacks is 6" × 9". This is what readers expect when they pick up a novel, and it's the most commonly sold size in bookstores. 5.5" × 8.5" is an acceptable alternative that feels slightly more premium for some genres. Avoid 8.5" × 11" for fiction — it looks like a workbook, not a novel.
Does trim size affect the ISBN or ASIN?
No. Trim size is a physical attribute of your book, not an identifying characteristic for ISBN or ASIN purposes. Changing trim size on an existing KDP paperback (by uploading a new interior and cover) does not change the ASIN or require a new ISBN.
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