Book spine calculator for KDP paperbacks.
Enter the page count and the paper, and get the spine width in inches and millimetres, calculated with the factors Amazon KDP publishes.
Book spine calculator: formula, paper thickness and common mistakes
The spine width formula
Spine width = page count × paper thickness. The page count is rounded up to an even number because printers bind sheets of two pages each: 301 pages become 302.
Example: 300 pages on KDP cream paper make 300 × 0.0025 in = 0.75 in (19.05 mm). On white paper the spine is 0.676 in (17.16 mm).
Example: from spine to full cover width
A novel in 6 × 9 in has 250 pages on cream paper. The spine is 250 × 0.0025 in = 0.625 in (15.88 mm) wide.
The full cover width is then 0.125 + 6 + 0.625 + 6 + 0.125 = 12.875 in, the height 9.25 in. If the page count changes by ten pages, the spine changes by 0.025 in (0.64 mm).
Paper thickness at KDP and for bookstores
KDP publishes the thickness per page. For 50 lb white paper, bookstore printing uses a table whose values do not grow evenly. On white paper the spine comes out narrower there.
| Pages | KDP white | KDP cream | Bookstores white (50 lb) |
|---|---|---|---|
| 100 | 0.225 in (5.72 mm) | 0.25 in (6.35 mm) | 0.207 in (5.26 mm) |
| 200 | 0.45 in (11.44 mm) | 0.5 in (12.70 mm) | 0.424 in (10.76 mm) |
| 300 | 0.676 in (17.16 mm) | 0.75 in (19.05 mm) | 0.629 in (15.97 mm) |
| 400 | 0.901 in (22.88 mm) | 1 in (25.40 mm) | 0.821 in (20.86 mm) |
As of October 2026. KDP: white 0.002252 in, cream 0.0025 in per page (KDP Help, “Set up a paperback cover”). Bookstores: the printer's spine table for 50 lb white (as of September 2026). For cream and premium color paper in bookstore printing there are only estimates: the printer's cover template is binding.
Spine text: minimum pages and clearance
Whether title and author name fit on the spine depends on the page count.
- KDP: spine text from 79 pages, 0.0625 in (1.6 mm) clearance to each spine edge.
- Bookstores: spine text from 48 pages, also 0.0625 in (1.6 mm) clearance. For a spine under 0.35 in (8.9 mm), 0.03125 in (0.8 mm) is enough.
- Both: keep text and logos at least 0.125 in (3.2 mm) inside the trim line.
Common mistakes with spine width
- Taking the page count from your word processor instead of the finished interior PDF. Front matter and blank pages count.
- Not recalculating the cover after a change to the layout. 20 extra pages make the spine 0.045 in (1.14 mm) wider on KDP white paper.
- Switching paper without adjusting the spine. At 300 pages, cream paper is 0.074 in (1.89 mm) wider than white.
- Using the KDP factors for bookstore printing. At 300 pages on white paper, the two differ by 0.047 in (1.19 mm).
- Setting spine text with too few pages or without clearance to the spine edge.
Next step: the cover size
The spine width determines the full width of the cover. The KDP cover calculator gives you that size with bleed and a template, and the printing cost calculator the cost per copy.
How to use it
- Enter the page count Use the page count of your finished interior PDF, including blank pages and front matter.
- Choose paper and ink White or cream paper for black & white, or standard or premium colour.
- Read the spine width You get the width in inches and millimetres and whether text fits on the spine.
At a glance
- KDP spine factor for white paper: 0.002252 in (0.0572 mm) per page.
- 200 pages on white paper make a 0.45 in (11.44 mm) spine.
- KDP allows text on the spine from 79 pages.
How it is calculated
- Spine width = page count × paper factor.
- KDP factors per page: white paper 0.002252 in, cream paper 0.0025 in, standard colour 0.002252 in, premium colour 0.002347 in.
- Text on the spine needs at least 79 pages, and should keep 0.0625 in (1.6 mm) from each spine edge.
Source: Amazon KDP Help, “Cover calculator and templates” and paperback cover guidelines (kdp.amazon.com, retrieved October 2026).
Questions
How do I calculate the spine width for KDP?
Multiply the page count by the factor for your paper: 0.002252 in for white paper, 0.0025 in for cream. 300 pages on cream paper give a 0.75 in spine.
Does the page count include blank pages?
Yes. Count every page of the interior PDF, including blank and front-matter pages.
Is the hardcover spine the same?
No. Hardcovers have a different construction; use KDP's cover calculator for case laminate hardcovers.
How wide is the spine of a 100-page book?
On white paper 100 × 0.002252 in = 0.225 in (5.72 mm), on cream paper 0.25 in (6.35 mm). Narrow, but KDP allows spine text from 79 pages.
How wide is the spine when printing for bookstores?
For 50 lb white paper, bookstore printing does not use a fixed per-page factor but its own spine table. 200 pages come to 0.424 in (10.76 mm) there, compared with 0.45 in (11.44 mm) on KDP white paper. The printer's cover template is always binding. This calculator uses the KDP factors.
How many pages do I need for text on the spine?
KDP asks for at least 79 pages, bookstore printing for at least 48. Keep at least 0.0625 in (1.6 mm) free on each side of the spine text.
Why does the calculator use even page counts?
Printers bind sheets, and every sheet has two pages. If you enter 301 pages, the calculator works with 302.
Is the spine wider for color books?
Not for standard color: the factor is 0.002252 in, the same as white paper. Premium color is slightly thicker at 0.002347 in per page; 300 pages give 0.704 in (17.88 mm) instead of 0.676 in (17.16 mm).