Book & Print Tools › Spine width calculator

The spine is the narrow strip that joins your front and back covers. Its width depends on two things: how many pages the book has and how thick the paper is. Get it wrong by a few hundredths of an inch and the title can wrap onto the cover or sit off-centre.

This calculator multiplies your page count by the paper thickness per page. Thickness differs between white, cream and colour-printed paper, so pick the stock your printer will use. Page count means the printed pages in the finished book, front matter included, and a printer will round it up to an even number.

The result is shown in inches and millimetres. Very thin books (under 79 pages on KDP) cannot hold spine text, and the tool warns you when you are in that range. Use the result with the full cover size calculator to get the whole cover artwork size.

How to use it

1. Enter the final page count of your interior PDF.
2. Choose the paper type you will order.
3. Read the spine width, and send it to your cover designer.

Worked example

300 pages on white paper gives 300 × 0.002252 = 0.6756 in (17.16 mm).

Sources and figures

• Amazon KDP Help Center, paperback cover calculator figures

Figures checked against the source on 2026-10. Printers can change them, so confirm with your printer before ordering.

Questions

Why does paper type change the spine?

Cream paper is slightly thicker than white, and colour interiors use a different stock, so each page adds a different thickness.

Which page count should I use?

The total number of printed pages, including blank pages and front matter. Your PDF viewer shows it.

Is this accurate for every printer?

It uses KDP's published figures. Other printers publish their own, so check yours before sending the cover.

What if my result looks too thin for text?

Under about 79 pages most printers advise leaving the spine blank.

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