About the KDP Trim Size Calculator
Trim size is the finished size of your book, and it affects almost everything that follows: page count, spine width, cover size, printing cost and how the book feels in a reader's hands. Changing it after the interior is laid out means reformatting every page, so it pays to decide early.
This tool converts a standard or custom size into inches, millimetres and pixels at 300 DPI, reports orientation and aspect ratio, and tells you whether the size is a standard KDP option. It also flags large trim: any book wider than 6.12" or taller than 9". Large trim books cost more per page to print, which lowers your royalty at the same list price.
The table underneath lists every trim size configured on this site, with metric equivalents, trim class and whether it is offered for paperback, hardcover or both. When you have a size, check what it means for price with the Paperback Pricing Calculator.
How It Works
Pick a standard size or enter a custom width and height in inches or millimetres. Millimetres are converted at 25.4 mm per inch.
The size is compared with KDP's standard sizes. If it is not an exact match, the tool names the nearest standard size. Paperback custom sizes must be 4" to 8.5" wide and 6" to 11.69" tall.
Large trim is any width over 6.12" or height over 9". Pixels assume 300 DPI, the standard for print.
Formula
- Millimetres
- mm = inches × 25.4
- Pixels
- px = inches × 300
- Aspect ratio
- Ratio = width ÷ height
- Large trim
- Large if width > 6.12" or height > 9"
Example
A custom 150 × 230 mm paperback
- 150 mm ÷ 25.4 = 5.906" wide; 230 mm ÷ 25.4 = 9.055" tall.
- At 300 DPI that is 1,772 × 2,717 pixels per page.
- The height is over 9", so it is large trim.
- It is not a standard size; the nearest standard size is 6" × 9".
This custom size prints as large trim. Switching to the standard 6" × 9" keeps it at regular trim and lowers printing cost.
Important Notes
- Trim availability can vary by ink and paper type. Check the options KDP shows when you set up your book.
- Custom sizes are allowed for paperbacks but may not be eligible for Expanded Distribution.
- Pixel sizes are for one page without bleed. Use the KDP Bleed Calculator if your interior has bleed.
- Hardcovers are only available in a short list of sizes, shown in the table.
Frequently Asked Questions
What is the most common KDP trim size?
6" × 9" is the most common size in the US for both fiction and non-fiction. 5" × 8" and 5.5" × 8.5" are popular for novels and shorter books.
Why does large trim matter?
KDP charges a higher per-page printing cost for large trim books. On a long book that can add more than a dollar per copy, which comes straight out of your royalty.
Is 6.14" × 9.21" large trim?
Yes. It is wider than 6.12" and taller than 9", so it uses large trim pricing even though it looks close to 6" × 9".
Can I use A5 or A4?
A4 (8.27" × 11.69") is a standard KDP size. A5 (148 × 210 mm) is not standard, but you can enter it as a custom size and see the nearest standard option.
Does trim size change my page count?
Yes. A smaller page holds fewer words, so the same manuscript needs more pages, which widens the spine and raises printing cost.
Which sizes are available for hardcover?
Only the sizes marked Yes in the Hardcover column. If you plan both formats, choose one of those sizes for the paperback too so the editions match.
Related KDP Tools
- KDP Cover Size CalculatorGet full-wrap cover dimensions with a live back, spine and front diagram.
- KDP Bleed CalculatorCalculate interior page size with bleed for full-page images and backgrounds.
- KDP Margin CalculatorFind minimum gutter and outside margins for your page count and bleed setting.
- KDP Page Count CalculatorConvert word count to estimated pages, or pages to words, by trim and font size.
- KDP Spine Width CalculatorCalculate paperback spine width from page count and paper type.
- Image DPI CheckerRead pixel size, DPI metadata, print size and file details from an image.
Related Guides
- KDP Trim Sizes ExplainedEvery standard KDP trim size in inches and mm, the regular vs large trim rule and how it affects print cost, common sizes by genre, and how custom sizes work.
- KDP Bleed ExplainedWhat bleed is, KDP's 0.125" (3.2 mm) bleed requirement, how to size interior pages and covers with bleed, safe margins, and when your book needs bleed at all.