Where do the numbers come from?

KDP's published paper thicknesses for paperbacks: 0.002252 in a page for white paper and standard colour, 0.0025 in for cream, 0.002347 in for premium colour. The cover adds 0.125 in of bleed on every outside edge.

Does it work for IngramSpark or Lulu?

Only roughly. Their papers differ slightly, so use their own calculator for the final file.

Is it for hardcovers?

No, paperbacks only. KDP hardcovers add the boards and a wider wrap; use KDP's hardcover template.

Is anything I type sent anywhere?

No. The sums are done in your browser.

Spine width calculator

For KDP paperbacks: enter the page count, paper and trim. You get the spine and the whole cover size, then see the book in 3D.

Page countPaperTrim size

Spine 0.676 in (17.16 mm)

Full cover with bleed: 12.926 × 9.250 in (328.3 × 234.9 mm), 3878 × 2775 px at 300 dpi.

Long enough for spine text.

The cover laid flat, to scale. The orange band is the spine; inside the dashed line is what’s left after trimming.

See it as a 3D book

How it works, with worked examples: KDP spine width, explained.

Questions people ask.

Where do the numbers come from?: KDP's published paper thicknesses for paperbacks: 0.002252 in a page for white paper and standard colour, 0.0025 in for cream, 0.002347 in for premium colour. The cover adds 0.125 in of bleed on every outside edge.
Does it work for IngramSpark or Lulu?: Only roughly. Their papers differ slightly, so use their own calculator for the final file.
Is it for hardcovers?: No, paperbacks only. KDP hardcovers add the boards and a wider wrap; use KDP's hardcover template.
Is anything I type sent anywhere?: No. The sums are done in your browser.