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Spine Width & Cover Size Calculator

KDP paperback spine width is page count × a per-paper thickness. Enter your specs and get the exact full-cover canvas size (with bleed) to hand your cover designer.

KDP paperbacks: 24-828 pages.
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spine width (inches)
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spine width (mm)
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full cover w/ 0.125" bleed
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pixels @ 300 DPI

Full cover = bleed + back + spine + front + bleed. Spine text needs 79+ pages (KDP rule); leave 0.0625" margin either side of spine text.

How to calculate your paperback spine width

01
Enter your final page count
Use the page count of your formatted PDF interior, not your manuscript word count. KDP paperbacks must be 24-828 pages.
02
Pick your paper type
White paper: 0.002252 inches per page. Cream: 0.0025 inches. Standard color: 0.002347 inches. Cream paper makes a thicker spine than white at the same page count.
03
Pick your trim size
The trim size you chose in KDP (6" x 9" is the most common for fiction).
04
Use the full-cover dimensions
Give your designer the full cover size including 0.125" bleed on each edge — the calculator outputs it in inches and in pixels at 300 DPI.

Frequently Asked Questions

How is KDP spine width calculated?

Multiply your page count by the per-page thickness of your paper: white paper 0.002252", cream 0.0025", standard color 0.002347". A 300-page book on white paper has a spine of 300 x 0.002252 = 0.6756 inches.

How many pages do I need for spine text on KDP?

Amazon requires at least 79 pages before you may print text on the spine, and spine text must leave at least 0.0625" of clearance on each side. Under 79 pages, leave the spine blank.

What size should my full paperback cover be?

Full cover width = bleed (0.125") + back cover width + spine width + front cover width + bleed (0.125"). Height = trim height + 0.25" of bleed. For a 300-page 6"x9" book on white paper that is 12.926" x 9.25" — 3878 x 2775 pixels at 300 DPI.

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