KDP Spine Width Calculator

Enter your page count and paper type to get the exact spine width KDP uses for your paperback cover, and whether your book is thick enough for spine text.

How spine width is calculated

KDP multiplies your page count by a fixed thickness per page for each paper type. The result is the width of the spine strip between your back and front cover.

spine width = page count × paper thickness per page

Paper	Per page (inches)	Per page (mm)
Black & white, white paper	0.002252	0.0572
Black & white, cream paper	0.0025	0.0635
Standard color, white paper	0.002252	0.0572
Premium color, white paper	0.002347	0.0596

Worked examples

120 pages, black & white, cream paper: 120 × 0.0025 = 0.3000" (7.62 mm). Spine text is allowed.
300 pages, black & white, white paper: 300 × 0.002252 = 0.6756" (17.16 mm). Spine text is allowed.
64 pages, premium color, white paper: 64 × 0.002347 = 0.1502" (3.82 mm). Spine text is not allowed.

Tips for designing the spine

KDP allows about 0.0625" (1.6 mm) of movement on either side of each fold line when books are trimmed and bound. Keep spine text at least that far from the spine edges, and avoid hard lines or a contrasting colour block that ends exactly at the fold, because a small shift becomes very visible. A background that runs smoothly across the spine onto the front and back hides that variation.

If you change your interior after making the cover, recalculate. Adding a 20-page appendix to a 200-page book on cream paper widens the spine by 0.05", which is enough to push spine text off-centre. Once you know the spine width, the cover size calculator gives the full wrap dimensions in inches and pixels.

Frequently asked questions

Why does cream paper make a wider spine?

Cream paper is slightly thicker than white paper. KDP uses 0.0025" per page for cream and 0.002252" for white, so a 300-page book is about 0.07" wider on cream.

Can I put text on the spine?

Only if your book has more than 79 pages (80 or more, since page counts are even). Thinner spines are too narrow for text to line up reliably, and KDP will reject the cover.

Do blank pages count?

Yes. Every page in your uploaded interior PDF counts, including blank pages, front matter and the back matter. If you are unsure, use the page count KDP shows after you upload the interior.

Does trim size change the spine width?

No. Spine width depends only on page count and paper. Trim size changes the front and back cover size, which you can work out with the cover size calculator.

Sources

KDP: Create a paperback cover

Rates last checked against KDP's help pages on 2026-10-16.