KDP Spine Width Calculator

Enter your page count, paper type, and binding to get the exact spine width and cover dimensions for your Amazon KDP paperback or hardcover cover.

How KDP spine width is calculated

Amazon uses a simple formula based on page count and paper stock thickness. Paperback spines are the page count times the paper thickness; hardcover (case laminate) spines add an allowance for the cover boards:

Cream paper is slightly thicker than white, resulting in a wider spine for the same page count. Cream paper is only available for paperback — hardcover (case laminate) uses white paper exclusively. The spine width determines whether you can include text on the spine (requires 79+ pages) and affects the total cover width calculation.

Total cover width formula

Hardcover covers are wider and taller than paperback covers for the same trim size. Each panel is 0.197" wider and 0.236" taller than the trim size, and 0.591" (15 mm) of wrap folds around the boards on all four edges in place of bleed. The 0.394" (10 mm) hinge beside the spine is part of each panel: keep text and important artwork out of it, because the cover flexes there.

For a 6×9 paperback with 200 pages on white paper, the spine is 200 × 0.002252 = 0.4504 inches, so the total cover width would be: 0.125 + 6 + 0.4504 + 6 + 0.125 = 12.7004 inches. The same book as a hardcover has a 0.639 inch spine, so the total cover width would be: 0.591 + 6.197 + 0.639 + 6.197 + 0.591 = 14.214 inches.

Important spine text rules

KDP allows spine text only when the spine is wide enough — this requires a minimum of 79 pages. Even then, keep all spine text within the spine safe zone (centered, with margin on both sides) to prevent it from wrapping onto the front or back cover during printing. Use a clean, readable font at a size that fits comfortably within the spine width.

Related resources

See our complete KDP cover size guide for all paperback and hardcover trim sizes with bleed specs and paper types. If your cover was rejected by Amazon, check our guide to the 8 most common KDP cover rejection reasons and how to fix each one.