KDP Cover Builder
Join your front and back covers with a correctly sized spine. Preview locally, then download PNG or PDF.
Free. No sign-up. Your images stay in your browser.
1Book
Binding
Reading direction
Size shortcuts
KDP's A4 preset is 8.27 × 11.69 in = 210.06 × 296.93 mm, not exact ISO A4 (210 × 297 mm).
Interior paper changes the spine width, even though the cover itself always prints in colour.
108 pages / 54 sheets. Count every page in the final interior PDF, blanks and front matter included — not the last page number.
Cover size
- Spine
- 0.2432 in · 6.18 mm
- Full cover
- 17.0332 × 11.94 in
- At 300 PPI
- 5,110 × 3,582 px
KDP rules checked 2026-10-08. KDP can change them; check its cover calculator before you publish.
2Artwork
Drop both images here together, or one on each slot. Your images stay in this browser.
Back cover
left of spineDrop a PNG or JPEG here
Front cover
right of spineDrop a PNG or JPEG here
Swaps which image is the back and which is the front, with their crops. It never mirrors the artwork.
3Spine
Spine colour #000000 · RGB 0, 0, 0
Advanced: extend the transition into the covers
This changes your cover artwork near the spine. Check the preview closely.
Outside of the cover · back | spine | front
Add your back and front cover images to fill the panels.
Updating…Guides and legend
Guides and the darkened bleed are on screen only. They are never in the PNG or PDF you download. On-screen colours can differ from print.
Developer check: compare with a KDP template
Optional. Lay a template from KDP's cover calculator over the preview to check the folds, spine and barcode by eye. It stays on screen only and is never part of your download.
Download
Fix book settingsHigher resolution creates more pixels and a larger file. It cannot restore detail missing from the original images.
Upload the PDF to KDP as your print cover. The PNG is for editing and archiving.
Preflight
Before you upload
- Inspect the crop and the safe-area guides on both covers.
- Check the barcode area is clear.
- Confirm your final interior PDF has exactly 108 pages.
- Upload the PDF and review it in KDP Previewer.
- Consider ordering a printed proof copy: screen colours (RGB) can shift in print.
This tool cannot check text inside your artwork, your ISBN, or whether you own the content. Exports are sRGB; this is not a colour-proofed CMYK or PDF/X file.
File options
Barcode
Cover finish (a note for you; it does not change the size)
Before you rely on this: Use this as a quick guide and check the result against your own working before you rely on it.
How to use this calculator
- Choose the binding, trim size, interior ink and paper, and your final interior page count. The cover size updates as you go.
- Add your back cover and front cover images (PNG or JPEG). Drop them in together or one at a time; nothing is uploaded.
- Pick a spine: a solid colour, a colour sampled from either cover, the back or front texture continued across the spine, or a blend of both.
- Check the preview with the trim, fold, safe-area and barcode guides on, and fix anything the preflight panel lists.
- Choose a resolution and download the PDF for KDP. The PNG is there for editing and archiving.
How it works
A paperback cover is back + spine + front with 0.125 in of bleed all round. The spine is your page count multiplied by KDP's per-page paper thickness: 0.002252 in for white paper and standard colour, 0.0025 in for cream, 0.00235 in for groundwood and 0.002347 in for premium colour. A 108-page A4 book on white paper has a 0.243216 in (6.18 mm) spine and a 17.033 × 11.94 in cover.
A hardcover is a case sheet, not a paperback with a wider spine: visible boards 5 mm wider and 6 mm taller than the trim, a 15 mm wrap that folds inside the boards, 10 mm hinges beside the spine, and a spine 4.8 mm wider than the paper alone. These numbers were measured from KDP's own cover calculator and templates, not estimated.
Your images are placed proportionally (Cover crops the overflow, Contain shows everything), the bleed is filled from the artwork's own edge pixels, and the spine is built from local pixels — nothing is generated by AI. The download is drawn from your original files at the resolution you choose, with no guides, labels or watermark in it.
Everything happens in your browser: decoding, the preview, the spine, the PNG and the single-page PDF. Your images and settings are never uploaded.
Worked example
A4 paperback, 108 pages, black ink on white paper. Spine = 108 × 0.002252 in = 0.243216 in (6.18 mm). Full cover = 8.27 + 0.243216 + 8.27 + 2 × 0.125 = 17.033216 in wide by 11.69 + 0.25 = 11.94 in tall. At 300 PPI that is 5,110 × 3,582 pixels, and the PDF page is 1,226.39 × 859.68 points.
Common mistakes
- Using the last printed page number instead of the total page count of the interior PDF — blank pages and front matter count too.
- Choosing a different paper than the interior will print on. Cream paper makes a thicker spine than white, so the cover would not fit.
- Putting titles or logos in the bleed, the hinge or the barcode box, where they can be trimmed, folded or covered.
- Expecting 600 DPI to sharpen a small image. A higher setting adds pixels, not detail; check the PPI your images actually provide.
- Uploading the PNG to KDP. KDP's print cover upload takes a single PDF — use Download PDF for KDP.
Frequently asked questions
Can I use A4 or A5?
Paperback supports the KDP A4 preset (8.27 × 11.69 in) and A5 as a custom trim where the selected print settings are valid. Hardcover uses a shorter set of supported sizes; 8.25 × 11 in and 5.5 × 8.5 or 6 × 9 in are the closest to A4 and A5.
Why does paper type matter?
Different interior papers create different spine thicknesses. Use the same ink and paper settings as the final book, even though the cover itself always prints in colour.
Pages or sheets?
Enter all interior PDF pages, including blanks and introductory pages. Two pages equal one sheet, so 54 sheets is 108 pages.
Does 600 DPI make blurry artwork sharp?
No. It creates a larger export, but the detail is limited by your source images. The tool shows the PPI each image really provides at your book size.
Which file do I upload to KDP?
Use the single-page PDF for the print-cover upload. The PNG is useful for editing and archiving.
Do my images leave my computer?
No. Decoding, the preview, the spine and both exports run in your browser. Nothing is uploaded, and projects are only kept on your device if you choose Save project or Remember this project.
Will KDP accept my cover?
This tool sizes the cover to KDP's published rules and checks what it can, but only KDP can approve a book. Check the result in KDP Previewer and consider ordering a proof. Its colours are sRGB, not a colour-proofed CMYK file, so print colours can shift.
Do KDP's rules change?
They can. The sizes and spine formulas here were checked against KDP's help pages and cover calculator on 8 October 2026, and the page shows that date.
Related tools
- KDP Spine Width Calculator
- KDP Manuscript Checker
- Image Resizer
- KDP Interior Randomizer
- KDP Interior Repeat Builder
- Image DPI / Print Size Calculator
Explore more in PDF, Image, File, Data & Developer Tools.
Cite this tool
Zerdly. (2026). KDP Cover Builder. Retrieved from https://www.zerdly.com/tools/kdp-cover-builder/
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.