Book spine width calculator
Fablemora's spine calculator gives the spine width and full cover size for a paperback from its page count, paper and trim. It uses Amazon KDP's own per-sheet thickness — 0.002252″ white, 0.0025″ cream — adds no constant, and refuses any page count KDP will not bind on that paper, such as cream above 776 pages.
- Spine width
- 0.676″
- 17.16 mm
- Full cover
- 12.926 × 9.250″
- 32.8 × 23.5 cm
- Back, spine and front, with 0.125″ bleed on all four edges
- Long enough for spine text. KDP sets it from 80 pages up.
- Even page count, which is what a bound book has.
The numbers, and where they come from
Spine width is the page count times the thickness of one sheet. That thickness is a property of the stock, so it is the one number a calculator must not guess. These are Amazon KDP's, and they are the same constants this engine uses to lay out covers it has printed.
| Paper | Thickness per page | Pages KDP will bind |
|---|---|---|
| White | 0.002252″ | 24–828 |
| Cream | 0.0025″ | 24–776 |
| Premium colour | 0.002347″ | 24–828 |
| Standard colour | 0.002252″ | 72–600 |
Why there is no extra 0.06 inch
Nearly every free calculator adds 0.06″ to the spine for cover stock. That is an IngramSpark and Lulu convention, and a KDP cover built with it comes back rejected — the spine is too wide and the cover no longer lines up with the trim. There is no additive constant here, because KDP does not use one.
IngramSpark does not publish a formula
This is the part the other calculators invent. IngramSpark's File Creation Guide gives no per-page caliper: it tells you to use their Cover Template Generator, which builds the file from the stock they will actually put your book on — and the guide states plainly that they may substitute a paper weight and adjust the spine themselves. What they do publish is the geometry your artwork has to respect.
- Spine type safety, spines 0.35″ and wider
- 0.0625″ / 2 mm
- Spine type safety, spines under 0.35″
- 0.03125″ / 1 mm
- No spine text on perfect bound below
- 48
- Bleed, all sides
- 0.125″ / 3 mm
Read from IngramSpark's own File Creation Guide.
Why it refuses instead of answering
A 700-page cream 5×8 has a spine and no printer: KDP's cream band stops at 776 pages and colour stops at 600. A calculator that multiplies anyway gives you a number you believe, design around, and discover is worthless at upload. The bands are checked against the ink and the paper together, because they are different questions — the classic mistake is checking the trim alone.
Or skip the arithmetic
Fablemora builds the cover from these numbers: back, spine and front as one print-ready PDF, sized to your page count and stock, with the spine lettered when it is wide enough to carry type.
Make a book