Home Resources Spine width calculator
Free toolBook spine width calculator
Page count, trim size and paper stock in. Spine width out, in inches and metric, with the full wrap cover size for a paperback. The paper thicknesses are Amazon KDP's own published figures.
Off the final interior PDF, not the manuscript.
Changes the wrap, not the spine.
Most novels print black on cream.
Spine width
Page count × paper thickness, and nothing else. Trim size is not in that sum, so changing it moves the wrap and leaves the spine where it is. Trim does change the spine, but only by changing your page count first: work that out here.
This runs entirely in your browser. Nothing you type is sent anywhere, and there is no account to make.
How to calculate spine width
Spine width = page count × paper thickness. The thickness of one printed sheet, which depends on the stock and not on the binding:
| Paper | Inches per page | Millimetres per page |
|---|---|---|
| Black ink on cream | 0.0025 | 0.0635 |
| Black ink on white | 0.002252 | 0.0572 |
| Standard colour, paperback only | 0.002252 | 0.0572 |
| Premium colour | 0.002347 | 0.0596 |
Spine width at common page counts
Black ink, the two paper stocks a novel is printed on.
| Page count | Cream paper | White paper |
|---|---|---|
| 100 pages | 0.25 in / 6.3 mm | 0.225 in / 5.7 mm |
| 150 pages | 0.375 in / 9.5 mm | 0.338 in / 8.6 mm |
| 200 pages | 0.5 in / 12.7 mm | 0.45 in / 11.4 mm |
| 250 pages | 0.625 in / 15.9 mm | 0.563 in / 14.3 mm |
| 300 pages | 0.75 in / 19.0 mm | 0.676 in / 17.2 mm |
| 350 pages | 0.875 in / 22.2 mm | 0.788 in / 20.0 mm |
| 400 pages | 1 in / 25.4 mm | 0.901 in / 22.9 mm |
| 450 pages | 1.125 in / 28.6 mm | 1.013 in / 25.7 mm |
| 500 pages | 1.25 in / 31.8 mm | 1.126 in / 28.6 mm |
| 600 pages | 1.5 in / 38.1 mm | 1.351 in / 34.3 mm |
Paperback
Full wrap = bleed + back cover + spine + front cover + bleed. The bleed is 0.125 in on every outside edge, so the wrap is always 0.25 in wider than the two covers plus the spine, and 0.25 in taller than the page.
Spine text has two rules on top. KDP refuses it under 79 pages, and above that it wants 0.0625 in of clearance on each side of the text, because the fold lands in a slightly different place on every copy.
Hardcover
A case laminate cover is not a paperback with a thicker spine. KDP documents three allowances and generates the finished canvas itself:
- Wrap of 0.51 in (15 mm) past every outside edge, which folds around the board and glues to the inside.
- Spine hinge of 0.4 in (10 mm) each side of the spine, where the case bends open. No text and no barcode goes in it.
- Safe area starting 0.635 in (16 mm) from the edge of the book.
What Amazon does not publish is how far the case board overhangs the book block, and that number is inside the total cover size. So this gives you the spine and the allowances, and their own cover template generator gives you the canvas. Hardcover runs 75 to 550 pages, on white or cream, and standard colour is not offered.
The page count is the input everything else hangs off, and it is the one most people guess at. Turn a word count into a page count first if you do not have a laid-out interior yet. Galley reads the real page count straight off the print PDF it builds, so there is nothing to guess.
Everything here is Amazon's, for Amazon. IngramSpark prints on different stock and publishes its own template generator, and a spine width borrowed from one printer and sent to another is how you get a cover with the title creeping round onto the back.
For working things out, not for signing anything. Printers and retailers set their own rates and specifications, change them without notice, and none of them is affiliated with me or with Galley. I checked these figures by hand in August 2026 against KDP's paperback cover specification and its hardcover one . Confirm on the official page before you commit money to a price, a print run or a contract.
Questions
How do I work out the spine width of a book?
Multiply the page count by the thickness of one sheet of the paper you are printing on. On Amazon KDP that is 0.002252 inches a page for black ink on white paper and 0.0025 inches a page on cream. A 320 page novel on cream comes to a 0.8 inch spine, or 20.3 mm.
Is the page count the same as my Word document?
No, and this is where most covers go wrong. The page count is the page count of the final laid-out interior PDF, at your real trim size and type size. It moves every time the text reflows. Set the interior first, then read the page count off it, then design the cover.
How wide does the spine need to be for text on it?
On a paperback KDP will not print spine text below 79 pages. Above that, keep the text at least 0.0625 inches clear of each fold, because the trim shifts slightly on every copy. A hardcover has a 0.4 inch hinge on each side of the spine and nothing should sit in it.
Why does the hardcover not give me a full cover size?
Because Amazon does not publish one. KDP documents the wrap, the hinge and the safe area, then generates the finished canvas with its own template tool, which also accounts for how far the case board overhangs the book block. So this gives you the spine width and the published allowances, and stops there.
Does this work for IngramSpark?
No. Ingram prints on its own paper stocks with its own thicknesses, and it publishes a cover template generator that knows them. Use that one for Ingram rather than a number worked out from Amazon paper.
Next
More at the resources index.
Put all this into practice when you write your novel in Galley.
Launch Galley