How to Calculate KDP Cover Dimensions

What a KDP paperback cover file actually is

When you upload a paperback cover to KDP, you do not upload a front cover on its own. You upload a single PDF that wraps around the whole book. Reading from left to right, the file contains the back cover, the spine and the front cover. Around the outside of that spread sits a strip of bleed, extra artwork that gets trimmed off after printing so no white edges show.

That means three things decide your cover size: your trim size (the finished size of the book), your spine width (which depends on page count and paper) and the bleed KDP requires. Once you know those three numbers, the rest is simple addition.

The paperback cover formula

KDP asks for 0.125" (3.2 mm) of bleed on the top, bottom and both outside edges of a paperback cover. There is no bleed at the spine, because the spine sits in the middle of the spread. Put together, the formula looks like this:

Cover width = 0.125 + trim width + spine width + trim width + 0.125

Cover height = 0.125 + trim height + 0.125

Spine width is the only part that needs its own calculation. For a paperback it is the page count multiplied by the thickness of one page for your paper type. Black ink on white paper uses 0.002252" per page and black ink on cream paper uses 0.0025" per page. Our guide on how to calculate paperback spine width covers every paper type in detail.

Spine width = page count x thickness per page

To convert inches to pixels, multiply by the resolution. KDP asks for cover images of at least 300 DPI, so a 1" strip of your cover needs 300 pixels. To convert inches to millimetres, multiply by 25.4.

Worked example: a 6x9 paperback with 300 pages on white paper

Let us size a cover for a 6" x 9" paperback with 300 pages, printed in black ink on white paper. These are the same numbers our cover calculator produces.

1. Spine: 300 pages x 0.002252" = 0.6756" (about 17.16 mm).
2. Width: 0.125 + 6 + 0.6756 + 6 + 0.125 = 12.9256".
3. Height: 0.125 + 9 + 0.125 = 9.25".
4. Millimetres: 12.9256" x 25.4 = 328.31 mm wide, and 9.25" x 25.4 = 234.95 mm tall.
5. Pixels at 300 DPI: 12.9256 x 300 = 3878 pixels wide (rounded), and 9.25 x 300 = 2775 pixels tall.

If the same book were printed on cream paper, the spine would grow to 0.75" (300 x 0.0025) and the full width would become 13". That is why you should finalise your paper choice before your designer starts work.

Where to keep text and important artwork

Printing and trimming are never perfectly exact, so some artwork near the edges and the spine folds may shift slightly. Plan your layout with that in mind:

• Extend background colours and images all the way into the bleed area so no white line appears after trimming.
• Keep titles, author names and other important text well inside the trim line, away from the outer edges.
• Leave room on the back cover for the barcode area. KDP places a barcode on the back cover for you unless you supply your own.
• Spine text is only allowed on books with at least 79 pages, and it needs clearance of 0.0625" on each side of the spine.

How hardcover covers differ

Case laminate hardcovers are built differently. The printed cover wraps around rigid boards and folds over their edges, and there are hinges where the cover bends near the spine. Instead of a 0.125" bleed, a hardcover file has a much wider wrap area, and each board is slightly larger than the trim size.

Our calculator estimates hardcover sizes using commonly published template measurements: a 0.591" wrap on each edge, boards about 0.197" wider and 0.236" taller than the trim, a 0.394" hinge, and a spine that adds a 0.189" allowance to the page thickness. For the same 6" x 9", 300-page white paper book, that gives an approximate hardcover cover of 14.4406" x 10.418".

Common cover size mistakes

• Designing at trim size only. A 6" x 9" front cover is not a KDP paperback cover. You need the full spread plus bleed.
• Using the wrong paper type. Cream paper is thicker than white, so the spine and full width change.
• Changing the page count after the cover is done. Even a few added pages alter the spine. Lock your interior first, then calculate the cover.
• Low resolution artwork. An image that looks fine on screen may print blurry. Check that your file is at least 300 DPI at full size.
• Forgetting the spine text rule. Books under 79 pages cannot have spine text, so leave that spine plain.
• Exporting the wrong file size. KDP accepts cover PDFs up to 650 MB, but the page size in the PDF must match the calculated dimensions.

Before uploading, run your final image through our Image DPI Checker and compare the dimensions with the calculator output. KDP's previewer will also flag many sizing problems, so read its warnings carefully.