Book spine calculator
Enter your page count and paper stock to get the spine width and the full flat cover size. Free, no sign-up.
The usual choice for non-fiction and most genre fiction.
Spine width
0.676″
300 pages × 0.002252″ per page
- Full cover widthBack + spine + front, including bleed
- 12.926″
- Full cover heightTrim height plus bleed top and bottom
- 9.250″
- On cream paperThe same book, the other stock
- 0.750″+0.074″
Don't know your page count yet? The margin calculator estimates it from a word count — or format the interior and it will tell you exactly.
The paper matters more than people expect
A spine is page count times the thickness of one sheet, and the sheets are not all the same:
| Paper | Per page | 300 pages |
|---|---|---|
| Black & white on white paper | 0.002252″ | 0.676″ |
| Black & white on cream paper | 0.0025″ | 0.750″ |
| Premium colour on white paper | 0.002347″ | 0.704″ |
Choosing cream over white adds nearly a tenth of an inch to a 300-page book. That is invisible in a spreadsheet and obvious on a shelf — and it is enough to push a spine title out of alignment if the cover was designed for the other stock.
Spine text needs 79 pages
Below that, KDP prints nothing on the spine. The band is too narrow to place type without risking it wrapping onto a face, so a novella or a short poetry collection gets a blank spine whatever the cover file says.
This is the kind of thing worth learning before commissioning cover art rather than after.
Use KDP's template to build the file
These figures come from KDP's published multipliers and are right for planning — whether a spine can carry a title, how a paper choice changes the design. When you actually build the cover, download KDP's own template for your exact trim and page count: it comes with the fold lines drawn on, and it is the file their checker expects.
Questions
- How is spine width calculated?
- Page count multiplied by the thickness of one sheet, which depends on the paper. KDP publishes a figure per stock: 0.002252 inches per page for black and white on white, 0.0025 on cream, 0.002347 for premium colour. There is no rounding and no minimum — a 120-page book on white has a spine of 0.27 inches.
- Why does cream paper make a thicker book?
- Because it is physically thicker paper. The same 300-page manuscript is 0.676 inches on white and 0.750 on cream — nearly a tenth of an inch wider. That is enough to matter on a cover, which is why the calculator shows you both.
- Why can't I put text on my spine?
- KDP will not print spine text below 79 pages. There is not enough width to place type without risking it creeping around onto the front or back, so thin books get a blank spine. Worth knowing before you design a cover around a spine title.
- What is bleed, and why is the cover bigger than the book?
- Bleed is the extra margin that gets trimmed off, so that anything meant to run to the edge actually does rather than leaving a white sliver. A cover is one flat sheet — back, spine, front — with 0.125 inches of bleed around the outside. There is no bleed between the panels, because they are not separate pieces.
- Do I need this if KDP has a cover template?
- KDP's template generator gives you the same geometry as a downloadable file, and you should use it when you actually build the cover. This is for the moment before that — checking whether a spine is wide enough for a title, or how much a paper choice will change the design, without going through a form for each variation.
The spine depends on the page count, and the page count depends on the interior. The print book formatter produces the interior and tells you exactly how long it runs — and the margin calculator covers the geometry inside the trim.