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Book spine width calculator
Your exact spine width for Amazon KDP — paperback or hardcover, in inches and millimeters — plus whether KDP will print your spine text. Same verified constants as KDP’s official cover calculator.
Need the full cover size, not just the spine? →
Spine width
0.676″
17.2 mm
Spine text
Allowed
KDP prints text at ≥ 0.0625″
Max text width
0.551″
14.0 mm
Math: 300 pages × 0.002252″ per page = 0.676″. Keep spine text at least 0.0625″ away from each spine edge so it can’t wrap onto the covers — that leaves 0.551″ for the text itself.
Or skip the spine math entirely.
publish.ai turns your finished manuscript into a complete KDP launch package — validated EPUB, designed covers, print-ready interior and wrap PDFs with the spine computed at these exact widths, Amazon listing copy, and launch graphics. One upload, minutes, from $29.99.
How spine width works
Paperback: the spine is simply pages × paper thickness. White paper adds 0.002252″ per page, cream 0.0025″, standard color 0.002252″, and premium color 0.002347″. KDP paperbacks run 24 to 828 pages.
Hardcover (case laminate): same page-block math, plus a fixed 0.189″ allowance for the rigid boards the cover wraps around. KDP hardcovers must be 76 to 550 pages.
Compute the spine last. Even a few added pages change the spine width and shift the whole cover layout — which is why designers tell you to lock the interior before touching the cover, and why authors end up paying $50 on Fiverr just to get spine alignment fixed after a late edit. Finalize your page count, then size the spine, then design.
This tool gives you the spine only. When you’re ready to build the actual cover file — full-wrap width, height, bleed, hinge, and barcode zone — use our full KDP cover size calculator.
Common questions
How is book spine width calculated?＋
Multiply your page count by the per-page paper thickness: 0.002252″ for black & white on white paper, 0.0025″ for cream paper, 0.002252″ for standard color, and 0.002347″ for premium color. Hardcovers (case laminate) add a 0.189″ board allowance on top of the page-block thickness. A 300-page cream paperback is 300 × 0.0025″ = 0.75″.
What is the minimum page count for spine text on KDP?＋
KDP only prints spine text when the spine is at least 0.0625″ wide — roughly 80+ pages for a paperback. Below that, submit a cover with a blank spine. Text must also sit at least 0.0625″ inside each spine edge, so your usable text width is the spine width minus 0.125″.
Does paper type change the spine width?＋
Yes. Cream paper is the thickest at 0.0025″ per page, so the same 300-page book is 0.75″ on cream but about 0.676″ on white paper — a difference of nearly 2 mm. Always pick your paper type before sizing the spine.
Why did KDP reject my spine text?＋
Usually the spine is under the 0.0625″ minimum, or the text sits closer than 0.0625″ to a spine edge and risks wrapping onto the covers. It also happens when the spine was computed for an old page count — even a few added pages shift the spine, so recalculate after every interior change.
Does this calculator work for IngramSpark books?＋
No — different printer, different paper stocks, different per-page thicknesses. Use IngramSpark's own cover generator for IS books. This calculator matches Amazon KDP exactly.