Calculate the full wrap dimensions, spine width, bleed, and 300 DPI pixel size for any KDP paperback — before you design or upload.
KDP's paperback cover guidelines lock the math: spine width = page count × paper-page thickness; full wrap width = 0.125" bleed + back trim + spine + front trim + 0.125" bleed; full wrap height = trim height + 2 × 0.125" bleed; pixel size = inches × 300 DPI for print-ready files.
White paper is 0.002252" per page, cream is 0.0025", color is 0.002347". A 300-page novel on white paper has a 0.6756" spine; the same book on cream paper has a 0.75" spine. That eighth-of-an-inch is the difference between a cover that passes KDP's first review and one that gets bounced for spine text drifting into the safe zone.
We compute the exact same numbers KDP's own calculator uses — and when you click "Generate a cover with these specs" we lock the wizard to the same trim and spine so the AI cover comes out at the right wrap size on the first generation. No re-rendering after the fact.
KDP's automated review checks the uploaded PDF's page size against the trim + page count you registered. If the spine width is off by more than ~0.05" the cover gets rejected with a "cover file does not match book size" error. The fix is to recalculate spine width with the exact paper type you selected for the interior, then re-export at the new wrap width.
White paper is thinner (0.002252" per page) and cream is thicker (0.0025" per page). On a 300-page book that's a 0.0732" spine difference — small in absolute terms, but enough to push spine text past the safe zone. Always recalculate spine width when changing paper type, even if page count stays the same.
Yes. KDP requires 0.125" of bleed on every outside edge of the full wrap. The bleed area gets trimmed during printing, but design elements (background colors, illustrations) must extend INTO the bleed to avoid white edges on the printed book.
KDP's minimum is 300 DPI at the full wrap size. For a 6 × 9 book, 300 pages, white paper: full wrap is 12.9256 × 9.25 inches → 3878 × 2775 pixels. Below 300 DPI the print looks soft; above 300 DPI is fine but file size grows fast.
Linearly. Each additional page on white paper adds 0.002252" to the spine. So adding 50 pages adds about 0.113" to the spine. If you change page count after designing the cover (e.g. after copyediting), you MUST recalculate and re-export.
Yes for novels, memoir, and most non-fiction. Romance is often 5 × 8 or 5.5 × 8.5. Fantasy and sci-fi sometimes use 6.14 × 9.21 to match traditional publishers. Children's books vary widely (often square — 8.5 × 8.5). Pick the trim that matches your genre's shelf reality.
When you click "Generate a cover with these specs," our AI generator uses the exact wrap width as a hard layout constraint — so the spine text, back blurb area, and front composition all hit the right print zones. Without these specs the wizard defaults to a 6 × 9 / 300 pages / white paper setup, which most authors then have to re-export at a different size.
No. Spine width depends only on page count and paper type, not on whether the interior has color images. (Interior color does affect KDP's royalty math and printing cost — that's separate.)