Free KDP tool
KDP Cover Calculator: Spine Width and Cover Size
Pick your trim size, type your page count, choose your paper. This free KDP cover calculator gives you the spine width and the full paperback cover size with bleed, in inches or millimeters, plus the pixel size at 300 DPI, all from KDP’s own published formula.
By Corey Jackson, developer of Lacuna
Reviewed by Melissa Erin Jackson, author of 15 self-published books
Updated October 5, 2026 · Read about us
- Spine width
- 0.676 in
- Full cover width
- 12.926 in
- Full cover height
- 9.250 in
- Cover bleed
- 0.125 in on the top, bottom, and outside edges. Every KDP cover has it.
- Cover image size at 300 DPI
- 3,878 x 2,775 pixels, KDP’s minimum resolution
- Spine text
- Allowed. Keep it within 0.551 in, leaving 0.063 in clear on each side of the spine.
- Interior gutter (inside margin)
- At least 0.500 in for 300 pages. See the full gutter table
- Interior outside margins
- At least 0.250 in on the top, bottom, and outside
- Interior PDF page size
- 6.000 in x 9.000 in, the same as the trim
- Trim size
- 6 x 9 in
Unrounded inside, rounded for display. KDP’s own calculator is the final word before you upload.
How the math works
None of these numbers are ours. Every one comes from KDP’s paperback cover and trim size help pages, and we checked them on 2026-10-05.
Spine width
spine = page count x thickness of one page
Every page in your interior PDF counts, blank pages included. The thickness depends on the paper you pick when you set up the book in KDP.
Full cover size
width = 0.125 + trim width + spine + trim width + 0.125
height = 0.125 + trim height + 0.125
The 0.125 inches (3.2 mm) on each outside edge is bleed. KDP trims it off after printing, so your background has to run all the way out to it.
Thickness of one page, by paper
| Paper and ink | Per page (in) | Per page (mm) | Spine at 300 pages |
|---|---|---|---|
| Black ink, white paper | 0.002252 | 0.0572 | 0.676 in |
| Black ink, cream paper | 0.0025 | 0.0635 | 0.750 in |
| Standard color ink, white paper | 0.002252 | 0.0572 | 0.676 in |
| Premium color ink, white paper | 0.002347 | 0.0596 | 0.704 in |
The spine column follows the page count and trim size in the calculator above. KDP also lists a groundwood paper for black ink books, but publishes no spine thickness for it, so it is not offered here. Use KDP’s calculator for groundwood.
Trim sizes KDP accepts
KDP’s 17 paperback presets. Tags mark the UK and European sizes hiding behind odd inch numbers.
Small
Under 5.5 in wide
- 5 x 8 in127 x 203 mm
- 5.06 x 7.81 in129 x 198 mmB-format
- 5.25 x 8 in133 x 203 mm
Standard
5.5 to 6.12 in wide, up to 9 in tall
- 5.5 x 8.5 in140 x 216 mm
- 5.83 x 8.27 in148 x 210 mmA5
- 6 x 9 in152 x 229 mm
Large
Over 6.12 in wide or 9 in tall; costs more to print
- 6.14 x 9.21 in156 x 234 mmRoyal
- 6.69 x 9.61 in170 x 244 mm
- 7 x 10 in178 x 254 mm
- 7.44 x 9.69 in189 x 246 mmCrown Quarto
- 7.5 x 9.25 in191 x 235 mm
- 8 x 10 in203 x 254 mm
- 8.25 x 6 in210 x 152 mm
- 8.25 x 8.25 in210 x 210 mm
- 8.5 x 8.5 in216 x 216 mm
- 8.5 x 11 in216 x 279 mmUS Letter
- 8.27 x 11.69 in210 x 297 mmA4
The 80-page rule for spine text
79 pages or fewer
Blank spine
KDP won’t print spine text. Put the title on the front cover only.
80 pages or more
Spine text allowed
Keep it 0.0625 in (1.6 mm) from each spine edge. The fold can shift that much.
Why 80, not 79: KDP’s help page says “at least 79 pages” in one spot and “more than 79 pages” in another. 80 satisfies both.
Minimum inside margin (gutter) by page count
| Pages | Gutter (in) | Gutter (mm) |
|---|---|---|
| 24 to 150 | 0.375 | 9.6 |
| 151 to 300 | 0.5 | 12.7 |
| 301 to 500 | 0.625 | 15.9 |
| 501 to 700 | 0.75 | 19.1 |
| 701 to 828 | 0.875 | 22.3 |
Top, bottom, and outside margins need at least 0.25 inches, or 0.375 inches if the interior has bleed. The KDP print specs section of our KDP formatting guide walks through trim, bleed, and gutter in more detail.
Hardcovers, and checking with KDP
This page is for KDP paperbacks only. KDP publishes no hardcover spine formula; its hardcover help page points you to its own calculator and adds that the case wrap and hinge take extra room. For a hardcover, or to double-check any paperback before you upload, use KDP’s cover calculator and template generator. It is the final word. Our numbers come from the same formula on KDP’s cover page and trim size page, kept unrounded until display.
The cover is half the upload. Lacuna does the other half.
KDP checks the interior PDF against the same trim size, page count, gutter, and bleed you just typed in. Lacuna builds that file to those specs.
Trim size, inches or millimeters
Pick any KDP trim from the same groups as this page, or switch on Custom Size and type an exact width and height. One toggle flips the whole app between inches and millimeters, just like the calculator above.
Margins checked against KDP
The Print Page Margins panel compares your gutter and outside margins with KDP’s minimums for your page count and shows a check mark when they pass. Bleed amount and edges are set in the same panel, and margin guideline overlays show the safe zone, content area, and trim line in the preview.
Print and ebook from one project
Import your Word document once, style it with one of 32 pre-made styles, and export a print-ready PDF for KDP, an EPUB for every ebook store, and a DOCX. A desktop app for Windows, Mac, and Linux, so your manuscript stays on your own computer.
Click any screenshot to see it full size.
The trial is free and has no time limit, with every feature switched on. The one thing payment unlocks is generating the final files, so you can format the whole book and check every page before you spend $149, one time.
What authors are saying
Real authors. Real books. Formatted with Lacuna.
I’m a cover designer and interior formatter by profession and run my own small publishing press, so trust me when I say I’m picky and my standards are high. InDesign has always been the only program that formats for print with the level of customization I need. For years, I’ve used it for print and another program entirely for ebooks to get the results I wanted. When I saw Lacuna, I immediately went to check it out and within an hour from having downloaded the trial, I was hooked.
This gives me so much more freedom with print options than other formatting programs like Atticus or Vellum while still making ebooks a breeze. The ability to work from one file and have separate print and ebook settings is a complete gamechanger. I’m still learning my way around the program and loving every second.
JJ Carpenter
The Haunting of Kenmore Asylum
I originally checked out Lacuna because somebody in a KDP publishing group I belong to asked if anyone had tried Lacuna out yet. I published nine other books using a different formatter, but I wasn’t happy with it. I ended up taking a look at Lacuna even though I was pretty much sold on Atticus or Vellum. Once I started diving into Lacuna and saw the ease of use and flexibility, I was absolutely floored. It was a no-brainer, and I purchased Lacuna. Since then the program has only improved. Corey is amazing at fixing things and streamlining processes.
If you take a look at the book that I formatted with Lacuna you will see, it would be pretty difficult to do something like that with one of those other formatting programs. Plus they cost more. In my opinion Lacuna is already the best formatter on the market and only getting better. Thanks, Corey and Melissa, for making this available.
NextGen Victory Press
3-Minute Wrestling Devotionals for Rising Athletes
I tried numerous formatting methods and followed endless instructions from publishing websites, but nothing ever turned out right. Since finding Lacuna, everything has changed. I’ve been able to update all my manuscripts effortlessly and give them the professional look they deserve.
Lacuna helped me perfect one of my most cherished stories, The Magic Globe, and finally present it exactly as I envisioned. It’s truly been a game changer for my author journey.
Samuel Graham Astley
The Magic Globe
KDP cover and spine questions
What authors ask when they size their first paperback cover.
Format the interior to match
Download Lacuna free, import your manuscript, and build a print-ready PDF at the trim size, gutter, and bleed KDP expects. Pay $149 only when you are ready to export.
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