What is the formula for KDP spine width?

Page count × paper thickness. On white paper that's pages × 0.002252 in, on cream pages × 0.0025 in, on premium colour pages × 0.002347 in. A 300 page book on white paper has a 0.676 in spine.

Does the page count include blank pages?

Yes. KDP counts every page in your interior file, blanks and front matter included.

Can I put text on a thin spine?

KDP only allows spine text when the book has more than 79 pages. Below that, leave the spine plain.

Why is my spine wider on cream paper?

Cream paper is slightly thicker than white, so the same book is about 11% thicker on cream.

Is a hardcover spine the same?

No. KDP hardcovers add the boards and a wider wrap, so use KDP's hardcover template for those.

KDP spine width: how to calculate it

The spine of a KDP paperback is exactly as wide as its pages are thick, and KDP publishes the thickness of each paper. So the spine width is one multiplication: page count × paper thickness. Get it right and the title sits in the middle of the spine; get it wrong and it creeps round onto the front or back cover.

If you’d rather not do the sum, the spine width calculator does it and gives you the whole cover size too.

The thickness of each KDP paper

Paper	Per page (in)	Per page (mm)
White paper	0.002252	0.0572
Cream paper	0.0025	0.0635
Standard colour	0.002252	0.0572
Premium colour	0.002347	0.0596

These are KDP’s paperback figures. Other printers use their own paper, so an IngramSpark or Lulu book of the same length can come out slightly different: use their calculator for those.

Worked examples

Pages	White	Cream	Premium colour
100	0.225 in (5.7 mm)	0.250 in (6.3 mm)	0.235 in (6.0 mm)
200	0.450 in (11.4 mm)	0.500 in (12.7 mm)	0.469 in (11.9 mm)
300	0.676 in (17.2 mm)	0.750 in (19.0 mm)	0.704 in (17.9 mm)
400	0.901 in (22.9 mm)	1.000 in (25.4 mm)	0.939 in (23.8 mm)
600	1.351 in (34.3 mm)	1.500 in (38.1 mm)	1.408 in (35.8 mm)

The sample book The Quiet Coast as a 6 by 9 inch paperback with 100 pages on white paper, turned to its spine — The same 6 × 9 in paperback at 100, 300 and 600 pages on white paper: spines of 0.225, 0.676 and 1.351 in. Made in DudeCovers from the page count.

The sample book The Quiet Coast as a 6 by 9 inch paperback with 300 pages on white paper, turned to its spine — The same 6 × 9 in paperback at 100, 300 and 600 pages on white paper: spines of 0.225, 0.676 and 1.351 in. Made in DudeCovers from the page count.

From spine to the whole cover

The paperback cover file KDP asks for is one image: back cover, spine and front cover side by side, with 0.125 in of bleed on every outside edge. So:

Width = 0.125 + trim width + spine + trim width + 0.125
Height = 0.125 + trim height + 0.125

For a 6 × 9 in book of 300 pages on white paper: the spine is 0.676 in, and the cover is 12.926 × 9.25 in, which is 3878 × 2775 pixels at 300 dpi.

Text on the spine

KDP only allows spine text on books with more than 79 pages. A thinner book gets a plain spine, or a colour that carries on from the covers.
Keep spine text away from the folds: KDP asks for a little clear space on each side of it, so on a thin spine the type has to be small.
On books for the US and UK, spine text runs top to bottom, so it reads when the book lies face up.

Check it before you order a proof

Drop your finished cover into DudeCovers’s spine view and the spine is cut from your file at your trim size, so you can see the title sitting on the spine, or not, before you pay for a proof copy. Or start from a front cover alone, enter the page count, and see how thick the book will be.