KDP spine width calculator
Enter your page count, trim size and paper (white, cream, groundwood or colour). You get the spine width and the exact size your full cover PDF has to be — using Amazon's own formula, with nothing added to it. Custom trim sizes work too: 4" to 8.5" wide, 6" to 11.69" tall.
KDP takes widths from 4" to 8.5" and heights from 6" to 11.69".
Opens the generator with this exact book already set up. Nothing to re-type.
The formulas
Spine width = page count × paper thickness. Cover width = 0.125" bleed + back cover + spine + front cover + 0.125" bleed. Cover height = 0.125" + trim height + 0.125".
| Paper | Thickness per page |
|---|---|
| Black & white on white | 0.002252" |
| Black & white on cream | 0.0025" |
| Black & white on groundwood | 0.00235" |
| Premium colour | 0.002347" |
| Standard colour | 0.002252" |
KDP's help pages don't give a thickness for groundwood paper, only a warning that a cream book over 350 pages, or a white one over 525, needs a new cover if you switch. Their own cover calculator answers it: 0.235" of spine at 100 pages, 1.946" at 828, so 0.00235" a page (checked September 2026). That is thinner than cream and thicker than white. A 300-page book loses 0.045" of spine moving from cream to groundwood, and gains 0.029" moving from white.
KDP spine width by page count
The same formula, worked out for common page counts in black & white. The last column is the whole cover PDF for a 6" × 9" book on cream paper, bleed included. For any other count, trim or paper, use the calculator at the top.
| Pages | White | Cream | Groundwood | Full 6 × 9 cover, cream |
|---|---|---|---|---|
| 24 | 0.054" (1.4 mm) | 0.060" (1.5 mm) | 0.056" (1.4 mm) | 12.310" × 9.250" |
| 50 | 0.113" (2.9 mm) | 0.125" (3.2 mm) | 0.118" (3.0 mm) | 12.375" × 9.250" |
| 75 | 0.169" (4.3 mm) | 0.188" (4.8 mm) | 0.176" (4.5 mm) | 12.438" × 9.250" |
| 100 | 0.225" (5.7 mm) | 0.250" (6.3 mm) | 0.235" (6.0 mm) | 12.500" × 9.250" |
| 120 | 0.270" (6.9 mm) | 0.300" (7.6 mm) | 0.282" (7.2 mm) | 12.550" × 9.250" |
| 150 | 0.338" (8.6 mm) | 0.375" (9.5 mm) | 0.353" (9.0 mm) | 12.625" × 9.250" |
| 200 | 0.450" (11.4 mm) | 0.500" (12.7 mm) | 0.470" (11.9 mm) | 12.750" × 9.250" |
| 250 | 0.563" (14.3 mm) | 0.625" (15.9 mm) | 0.588" (14.9 mm) | 12.875" × 9.250" |
| 300 | 0.676" (17.2 mm) | 0.750" (19.0 mm) | 0.705" (17.9 mm) | 13.000" × 9.250" |
| 400 | 0.901" (22.9 mm) | 1.000" (25.4 mm) | 0.940" (23.9 mm) | 13.250" × 9.250" |
| 500 | 1.126" (28.6 mm) | 1.250" (31.8 mm) | 1.175" (29.8 mm) | 13.500" × 9.250" |
Custom trim sizes
KDP prints paperbacks at any custom size from 4" to 8.5" wide and 6" to 11.69" tall, not only the sizes in its menu (KDP help, "Print Options"). The cover formula doesn't change: twice the trim width, plus the spine, plus 0.25" of bleed across, by the trim height plus 0.25". Choose "Custom size" in the calculator above for any of them. These four are from KDP's own cover calculator at 200 pages of cream paper, a 0.5" spine (checked October 2026), and the calculator here gives the same figures:
| Trim | Full cover, 200 pages, cream | At 300 DPI |
|---|---|---|
| 4" × 6" | 8.75" × 6.25" | 2625 × 1875 px |
| 5.25" × 7.75" | 11.25" × 8" | 3375 × 2400 px |
| 7" × 10" | 14.75" × 10.25" | 4425 × 3075 px |
| 8.5" × 11.69" | 17.75" × 11.94" | 5325 × 3582 px |
The trim also sets the printing price. KDP counts a trim as large when it is more than 6.12" wide or more than 9" tall, and a large trim costs more to print per copy (KDP help, "Paperback Printing Cost"). For a custom size, the royalty calculator gives the right rate if you pick a menu trim in the same class: 6" × 9" or smaller for regular, 7" × 10" or larger for large.
Picture books: 24 and 32 pages in colour
A short colour picture book can be a paperback. KDP's minimums are 24 pages for a paperback in black ink or premium colour, 72 in standard colour, and 75 for any hardcover (KDP help, "Print Options"). Premium colour paper is 0.002347" a page, so the spine is 0.056" at 24 pages and 0.075" at 32: too thin for spine text. KDP's cover calculator gives a spine safe area of 0 at both counts. These full cover sizes are from KDP's own cover calculator (checked October 2026), and the calculator above gives the same with Premium colour picked; use "Custom size" for the square trims:
| Trim | 24 pages, premium colour | 32 pages, premium colour |
|---|---|---|
| 7.5" × 7.5" | 15.306" × 7.75" 4592 × 2325 px | 15.325" × 7.75" 4598 × 2325 px |
| 8.25" × 8.25" | 16.806" × 8.5" 5042 × 2550 px | 16.825" × 8.5" 5048 × 2550 px |
| 8.5" × 8.5" | 17.306" × 8.75" 5192 × 2625 px | 17.325" × 8.75" 5198 × 2625 px |
| 8" × 10" | 16.306" × 10.25" 4892 × 3075 px | 16.325" × 10.25" 4898 × 3075 px |
| 8.5" × 11" | 17.306" × 11.25" 5192 × 3375 px | 17.325" × 11.25" 5198 × 3375 px |
You don't need Cover Creator for the back. KDP takes your own cover as one PDF with the back, the spine and the front side by side, so the back can be a single picture. KDP adds a barcode to the back unless you supply one; the template above marks its box.
Inside margins change with thickness
The gutter — the inside margin, against the spine — has to grow as a book gets thicker, or the text disappears into the binding. KDP's table: 0.375" up to 150 pages, 0.5" to 300, 0.625" to 500, 0.75" to 700, and 0.875" beyond that. Outside, top and bottom need at least 0.25", or 0.375" if you use bleed.
What will it earn?
Spine width settles whether the cover prints. What it earns is a different sum: printing cost depends on page count, ink and trim size, and comes off your royalty. There is a royalty calculator here too — worth a look before you settle on a page count, because every page costs about a penny to print.
A free KDP cover template
The Download this cover template button above draws the whole cover as one PNG at 300 DPI, at the exact pixel size shown for your trim, page count and paper. On it: the 0.125" bleed in pink, the trim line, both spine folds, a dashed text-safe box 0.125" inside the trim (KDP asks for text at least that far in), the spine safe area once the book reaches 80 pages, and the 2" × 1.2" barcode box. Put it in Canva, Photoshop or Affinity as the bottom layer, design over it, then hide it before you export the PDF.
It is made in your browser and nothing is uploaded. Change the page count and download again. The spine and the full width change with it, so make a new template whenever the interior's page count changes.
Two rules people miss
Spine text needs 80 pages — and then it needs room. KDP's cover help page says "at least 79 pages" in one place and "more than 79 pages" in another, and Cover Creator's help says 80. In October 2026 a book KDP counted at 79 pages had its spine text refused, so plan on 80. Below that, leave the spine blank. From 80 it is allowed, but the text must stay 0.0625" inside each fold: KDP's cover calculator gives the spine's safe area as the spine width less 0.125". An 80-page book on cream paper has a 0.200" spine and a 0.075" safe strip — under 5pt of type. Readable 6pt type needs about 0.22" of spine: 88 pages on cream, 97 on white. Type laid out on exactly 0.0625" puts the bottom of a "g" on the line, so Puzzle Press keeps its spine text a further 1/64" in and starts printing it at 100 pages on cream, 111 on white. The calculator above shows the safe strip for your book.
Leave the barcode area clear. Keep a 2" × 1.2" clear space in the lower right of the back cover. Amazon prints a barcode there, and artwork underneath it will be covered.
Making a puzzle book?
Puzzle Press generates the whole paperback — word search, sudoku, maze, criss-cross or crossword puzzles with solutions, laid out to these specifications — and then the matching cover, with the spine already worked out from the page count of the book it just made. Free to use — pay only to remove the PREVIEW cover mark.
Make a book freeSee a finished book (PDF) · and its cover — made with it, nothing mocked up.
No sign-up. $19 once removes the PREVIEW cover mark; 30-day refund, no questions.
Making a handwriting workbook instead? Trace Press, from the same maker, lays out an A–Z letter tracing book and its cover to the same KDP rules. For a tracing book, the full cover width at every page count from 26 to 78 is worked out for all six trims on its tracing book cover size page.