What this calculator does
Amazon KDP prints a paperback cover as one flat wrap: back cover, spine and front cover side by side, with a little extra artwork around the outside that gets trimmed off. The size of that wrap depends on the trim size of your book, how many pages it has and what paper it is printed on. This calculator does the arithmetic so you can set up your cover canvas at the right size from the start.
The formulas
The spine is as thick as the pages stacked together, so:
Spine width = page count × paper thickness per page
The full wrap cover adds the bleed on both outer edges:
Cover width = 0.125 in + trim width + spine + trim width + 0.125 in
Cover height = 0.125 in + trim height + 0.125 in
The 0.125 inch (3.2 mm) bleed is extra artwork that extends past the trim line so nothing white shows if the cut lands slightly off.
Paper thickness per page
| Paper and ink | Inches per page |
|---|---|
| Black & white, white paper | 0.002252 |
| Black & white, cream paper | 0.0025 |
| Standard color | 0.002252 |
| Premium color | 0.002347 |
Cream paper is thicker than white, so the same book has a wider spine on cream. KDP revises its paper options from time to time and has added others, so treat these as planning numbers and confirm them against KDP’s own cover calculator before you upload.
A worked example
Take a 6 × 9 inch book with 200 pages on white paper. The spine is 200 × 0.002252 = 0.4504 inches. The cover width is 0.125 + 6 + 0.4504 + 6 + 0.125 = 12.7004 inches, and the height is 9 + 0.25 = 9.25 inches. At 300 pixels per inch, that is a canvas of 3811 × 2775 pixels. The same book on cream paper has a 0.5 inch spine, so the cover is a little wider.
| Pages | White paper spine | Cream paper spine |
|---|---|---|
| 100 | 0.2252 in | 0.2500 in |
| 200 | 0.4504 in | 0.5000 in |
| 300 | 0.6756 in | 0.7500 in |
Use the final page count
The most common mistake is calculating the spine before the interior is finished. Blank pages are real pages and they add thickness, so the number to use is the page count of the final interior PDF you will upload, not the count you planned at the start. If you add or remove even a few pages later, recalculate. A cover that is a fraction of an inch off can push the artwork around the spine fold, and KDP may reject the file or print it with the spine design misaligned.
Spine text and the barcode
Very thin spines cannot hold readable text. KDP’s guidance is to leave the spine blank on books of roughly 79 pages or fewer, and to keep spine text well inside the spine area on thicker books so it does not wrap onto the front or back. KDP also places the ISBN barcode on the back cover, so leave empty space there. Its template shows exactly where. Download that template for your final settings and lay your artwork over it.
Pixels at 300 DPI
The pixel values here assume 300 pixels per inch, a standard target for print. A canvas that size gives you the right resolution without any scaling. If you build the cover in a design tool that works in pixels, create the canvas at the pixel size shown. To verify that a cover image or any other image has enough pixels, use the Print Resolution Checker.
Limits
This calculator covers standard paperbacks. Hardcovers, special paper stocks and printers other than KDP have different numbers. The results are for planning, and KDP’s template generator is the final authority for your book.
Frequently asked questions
How do I calculate spine width for KDP?
Multiply your final page count by the paper thickness per page. For black and white on white paper that is 0.002252 inches, and for cream paper it is 0.0025 inches.
Why is the cover taller by 0.25 inches?
There is 0.125 inches of bleed above the book and 0.125 inches below it, so the height is the trim height plus 0.25 inches.
Does this work for hardcover?
No. Hardcover covers use a different layout with wrap margins and a hinge. Use KDP’s own calculator for those.
My page count is odd. Is that a problem?
A printed sheet has two sides, so page counts are normally even. Check the final count in the KDP previewer before you size the cover.
Are these numbers exact?
They use the published per-page thickness values and the standard bleed. KDP’s template generator is the final authority, so compare against it before uploading.