The numbers
| Ink and paper | Per page | Per page (mm) | 100 pages | 300 pages |
|---|---|---|---|---|
| Premium color · white paper | 0.002347 in | 0.0596 mm | 0.235 in | 0.704 in |
| Standard color · white paper | 0.002252 in | 0.0572 mm | 0.225 in | 0.676 in |
| Black & white · white paper | 0.002252 in | 0.0572 mm | 0.225 in | 0.676 in |
| Black & white · cream paper | 0.0025 in | 0.0635 mm | 0.25 in | 0.75 in |
| Black & white · groundwood paper | 0.00235 in | 0.0597 mm | 0.235 in | 0.705 in |
Hardcover spine = the same calculation + 4.8 mm, per KDP's cover calculator. The groundwood factor also comes from the cover calculator.
Paperback and hardcover spines
A paperback spine is exactly pages × factor. A hardcover spine is wider for the same book: KDP's cover calculator adds 4.8 mm, so a 300-page hardcover on cream paper has a 0.939 in spine against 0.75 in for the paperback.
Spine text
KDP allows text on the spine from 79 pages, with at least 0.0625 in (1.6 mm) between the text and each spine edge, and cover text must be at least 7 pt. On thin books these rules collide: at 80 pages on white paper the spine is 0.18 in wide, which leaves 0.055 in for the text.
By our calculation, a 7 pt line fits inside the spine margins from 100 pages on white paper, 90 on cream and 96 in premium color.
Why the cover comes last
The spine width, and so the width of the full cover, depends on the final page count and the paper. Every extra sheet (two pages) adds 0.0045 in on white paper. Finish the interior first, then build the cover from its real page count.
Example: a 300-page novel on white or cream paper
A 6 × 9 in novel with 300 pages has a 0.676 in spine on white paper and a 0.75 in spine on cream. Its full-wrap cover is 12.926 in wide on white paper and 13 in on cream, so a cover made for one paper doesn't fit the other.
Common mistakes
- Using a cover template made for another page count or paper.
- Adding spine text to a book under 79 pages. KDP doesn't allow it.
- Setting spine text right up to the folds, where it can wrap onto the front or back cover.
- Switching from white to cream paper (or back) after the cover is finished.
- Reusing the paperback spine width for the hardcover edition.
In kdpbook: kdpbook sizes the full-wrap cover PDF from the final page count and paper, and only adds spine text when the spine can hold it.