KDP Spine Width Calculator

Calculates a book spine width from page count and paper type for KDP cover setup.

100% FreeRuns in your browserBasic

Inputs

Paperback or hardcover spine width and full-cover size from KDP's published per-page thickness and its measured hardcover case model.

Enter the values and press Calculate.

Or load an example to see a worked result.

Your cover wrap

Schematic

Calculate with a trim size to draw your back, spine and front panels.

How the method works

Back, spine and front with bleed

Illustrative method

Keep trim, spine and bleed distinct. A 6 × 9 in paperback with 300 white-paper pages has a spine of 300 × 0.002252 = 0.6756 in; the full cover is 2 × 6 + 0.6756 + 2 × 0.125 = 12.9256 in wide and 9 + 2 × 0.125 = 9.25 in tall. KDP's own template is the final authority.

Fixed example values for illustration — not your result.

Before you rely on this: Estimates only — not financial, tax or legal advice. Confirm current rates, fees and rules before relying on these figures.

How to use this calculator

Enter your book's total page count, including blank pages (count pages, not sheets).
Choose the ink and paper you selected in KDP, and a trim size if you want the full cover dimensions.
Read the spine width and the full cover size with bleed, compare the other papers, and check it against KDP's own template.
The cover preview draws back, spine and front with the bleed band; the sizing worksheet and the paper comparison download as CSV. A custom trim can be typed in inches or millimetres.

How it works

Spine width = pages × KDP's per-page thickness: 0.002252 in for black ink or standard colour on white paper, 0.0025 in for cream, 0.00235 in for groundwood and 0.002347 in for premium colour.

Full paperback cover width = 2 × trim width + spine + 2 × 0.125 in bleed; height = trim height + 2 × 0.125 in. Inches are authoritative and mm = in × 25.4.

Page counts are checked against KDP's limits for the chosen trim and paper, and spine text is allowed from 80 pages. Hardcover is calculated as KDP's case sheet, not a paperback with a wider spine: spine = pages × per-page thickness + 4.8 mm, boards 5 mm wider and 6 mm taller than the trim, a 15 mm wrap all round and 10 mm hinges — a model measured from KDP's own cover calculator and templates (page counts 76–550; groundwood and standard colour are not offered for hardcover).

Worked example

A 300-page 6 × 9 in book on white paper. Spine = 300 × 0.002252 = 0.6756 in (17.16024 mm). Full cover = 2 × 6 + 0.6756 + 0.25 = 12.9256 in wide by 9.25 in tall. A 108-page book has a 0.243216 in spine.

Common mistakes

Counting sheets instead of pages, or leaving out blank pages.
Choosing the white-paper figure for cream paper.
Using paperback dimensions for a hardcover.

Tips

Count the total pages in your interior file, including blanks — not the number of sheets.
For a full print-ready cover layout, use the KDP cover builder.

Frequently asked questions

Why does my cover template show a slightly different number?

Always trust the template KDP generates for your trim size and page count. This tool follows KDP's published paperback rules, but KDP's own template is the final authority.

Does KDP put text on every spine?

No. KDP allows spine text only from 80 pages, because thinner spines can't print text reliably.

Does it work for hardcover?

No. Hardcover covers add hinge and wrap allowances that KDP supplies only in its hardcover template, so this tool does not estimate them.

Related tools

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Cite this tool

Zerdly. (2026). KDP Spine Width Calculator. Retrieved from https://www.zerdly.com/tools/kdp-spine-width-calculator/

Tip: Enter any known values to calculate the remaining results.

Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.