The spine is the one cover measurement you cannot choose. It is set entirely by two inputs — your final page count and your paper — and it then sets the width of your whole wraparound cover file. Get it wrong by a few hundredths of an inch and the spine text drifts onto the front or back cover, or the file is rejected outright. This page is the complete reference: every KDP factor, the IngramSpark PPI version of the same math, and the tables worked out so you can check any calculator’s answer by hand.
The KDP formula, for every paper
Spine width = page count × factor. KDP publishes one factor per ink-and-paper combination:
| KDP ink & paper | Factor (in per page) | 300-page spine |
|---|---|---|
| Black ink, white paper | 0.002252″ | 0.676″ |
| Black ink, cream paper | 0.0025″ | 0.750″ |
| Black ink, groundwood paper (Amazon.com) | 0.00235″ | 0.705″ |
| Standard color, white paper | 0.002252″ | 0.676″ |
| Premium color, white paper | 0.002347″ | 0.704″ |
Cream is the thickest of the black-ink papers — about 11% thicker per page than white — which is why the same manuscript is a visibly fatter book on cream, and why cream also lowers your maximum page count (see the page-count table). Paper choice and cover design are therefore one decision, not two: settle the paper first, then build the cover. Changing paper after the cover is built means rebuilding the cover.
The complete spine table (KDP and IngramSpark)
| Pages | White (KDP ×0.002252 / Ingram ÷444) | Cream (KDP ×0.0025 / Ingram ÷400) | Premium color (KDP ×0.002347) |
|---|---|---|---|
| 100 | 0.225″ | 0.250″ | 0.235″ |
| 200 | 0.450″ | 0.500″ | 0.469″ |
| 300 | 0.676″ | 0.750″ | 0.704″ |
| 400 | 0.901″ | 1.000″ | 0.939″ |
| 500 | 1.126″ | 1.250″ | 1.173″ |
| 600 | 1.351″ | 1.500″ | 1.408″ |
IngramSpark expresses the same thickness as PPI — pages per inch — for the specific stock in your title setup: spine = pages ÷ PPI. For the standard 50 lb paperback stocks (white 444, cream 400) the two systems are reciprocals and agree exactly. Where they part company is everywhere else: Ingram’s wider stock catalogue carries other PPIs, and your Ingram page count includes the mandatory blank final page, so the count itself can differ by one. The full Ingram-side story is in our IngramSpark spine width guide.
From spine to full cover size
The wraparound cover (paperback, both platforms) is: width = 0.125″ bleed + back cover + spine + front cover + 0.125″ bleed; height = trim height + 0.25″. A 300-page cream 6×9″ book is therefore exactly 13.000 × 9.25″; the same book on white is 12.926 × 9.25″. Hardcover covers are larger again — they wrap the boards — so build those from KDP’s hardcover template, not this formula. Our free spine width calculator runs all of this from your page count, paper, platform, and trim.
Check it yourself
- Count the file you will actually upload — final PDF pages, including front matter and blanks, not your word processor’s count.
- Multiply (KDP) or divide (IngramSpark) using the factor for your exact ink and paper from the tables above.
- Measure the cover PDF in Acrobat (File > Properties) and compare its total width against bleed + back + spine + front + bleed for your trim.
- Run the spine-text test: KDP allows spine text only at 79 pages or more, and the lettering must fit the safe strip — spine width minus 0.125″ (0.0625″ clearance each side). A 100-page white book’s strip is about 0.100″: legal, and effectively unreadable. See the spine text error guide.
Rather have the math checked against your actual files? The free check reads your interior and cover PDFs — spine, bleed, margins, fonts, barcode zone — and reports every finding in plain English, free within 48 hours. Get the free check →
The honest limit
These formulas reproduce the platforms’ published factors, and they are exact for the paperback stocks listed. They are still a check, not the authority: KDP’s cover calculator and IngramSpark’s template generator — each generated from your own title setup — are the final word for your book, and a template that disagrees with this table wins. If the two disagree by more than rounding, the usual cause is a different page count or a different stock in the title setup, and that mismatch is itself worth finding before you upload.
Or send us the files — the check is free
Email your interior and cover PDFs and we'll tell you exactly what's wrong — in plain English, free, within 48 hours. If it does need fixing, the by-hand fix is $19 and we redo it free if KDP rejects it for a formatting issue we were hired to fix. We rebuild files to be compliant with KDP's published spec — that's the promise we can keep.
Prefer the whole library in one file? The KDP Rejection Field Guide (free PDF) collects every guide, table, and the 13-point checklist.
More from the Help Library
- The KDP & IngramSpark Help Library — all guides & tools
- Spine width calculator — KDP and IngramSpark math, done for you
- IngramSpark spine width — pages ÷ PPI, in full
- Spine text error — too close to the edge, or a spine too thin for text
- White vs cream paper — thickness, page limits, and which suits your book
- Page count out of range — the minimum & maximum table
- The free rejection check — all 13 checks at once