---
title: "What Is Trim Size in Book Printing?"
description: "What a print book's trim size is, how it drives page count, printing cost and spine width on KDP, and how to set your manuscript up to match it."
url: "https://www.superebook.ai/glossary/trim-size"
updated: "2026-10-20"
---

# Trim size

**Definition.** Trim size is the finished width and height of a printed book's pages after the paper is cut. You choose it when you set up a paperback or hardcover on KDP, and it decides the page size of your interior file, how many pages the book runs to, its printing cost class and, through the page count, its spine width.

Sources checked October 20, 2026. Figures: KDP's paperback royalty rates, trim classes and spine figures, as of October 2026; KDP's Amazon.com paperback printing costs, as of October 19, 2026.

## How it works

KDP publishes a list of trim sizes, each with a minimum and maximum page count by ink and paper; its page calls 6 x 9 inches the most common paperback trim in the US. You set the trim as the page size in your writing or layout software before setting margins, because the margins depend on the page count and on whether anything bleeds. KDP prices print in two classes, and any trim wider than 6.12 in or taller than 9 in is a large trim with higher printing costs. Every printed book has at least 24 pages.

## An example

A manuscript that fills 180 pages at 6 x 9 inches fills more at 5 x 8, because each smaller page holds fewer words. More pages mean a wider spine, and past 110 pages they also mean a higher printing cost, since KDP's flat fee covers only 24 to 110 pages. Running the word count through a converter before choosing the trim avoids redoing the cover later.

## Common mistakes

Formatting the interior at US Letter or A4 and then choosing 6 x 9 on KDP, so the file is rejected or the text sits wrongly on the page. Picking a large trim without checking how much more it costs to print. And changing the trim after the cover is designed: the page count changes, so the spine width and the whole cover wrap change with it.

## Questions

**What trim size should a nonfiction paperback use?** 6 x 9 inches is a safe default: KDP calls it the most common trim for US paperbacks, and it is a regular trim, so it prints at the lower cost. Smaller trims suit short or pocket books.

**Can I change the trim size after publishing?** Changing trim means a new interior file and a new cover sized for the new page count. Plan it before the cover is made, and check the trim's page limits first.

## Sources

- [KDP: Set Trim Size, Bleed, and Margins](https://kdp.amazon.com/en_US/help/topic/GVBQ3CMEQW3W2VL6): Trim size defined, the trim list with page ranges, 6 x 9 as the most common US trim, setting trim before margins, the large-trim threshold.
- [KDP: Paperback Printing Cost](https://kdp.amazon.com/en_US/help/topic/G201834340): Different printing costs for large trim; the flat-fee page band.

## Related terms

- [Large trim](https://www.superebook.ai/glossary/large-trim.md)
- [Bleed](https://www.superebook.ai/glossary/bleed.md)
- [Gutter (inside margin)](https://www.superebook.ai/glossary/gutter.md)
- [Spine width](https://www.superebook.ai/glossary/spine-width.md)

## Read next

- [Word count to pages converter](https://www.superebook.ai/tools/word-count-to-pages-converter.md)
- [Self-publishing cost calculator](https://www.superebook.ai/tools/self-publishing-cost-calculator.md)
- [How long should an ebook be?](https://www.superebook.ai/guides/how-long-should-an-ebook-be.md)
- [All glossary terms](https://www.superebook.ai/glossary.md)