Changing a cover ought to be a two-minute job and frequently is not, because an EPUB stores the cover in more than one place and most tools update only the part they care about.
What an EPUB actually holds
An EPUB is a zip archive with a structure inside it. The cover exists as:
- An image file, usually in an images folder.
- A metadata entry pointing at that image as the cover.
- Often a cover page: an XHTML page that displays the image, which is what you see when you open the book at page one.
Replace only the image and a stale reference can remain. Replace only the metadata and the visible first page still shows the old artwork. That mismatch is the cause of nearly every "I changed it and it did not change" report.
The reliable route: Calibre
Calibre is free, handles all three places, and is what most people already have; what Calibre does well covers its wider role.
- Add the book to your Calibre library.
- Select it and click Edit metadata.
- In the cover box, Browse to your new image, or use Generate cover for a placeholder.
- Click OK.
- This is the step people miss: Calibre has now changed its *library* copy's metadata. To get a file with the new cover inside it, either Convert the book EPUB → EPUB, or right-click → Save to disk. Sending to a device also embeds it.
Converting EPUB to EPUB feels redundant and is the thing that actually rewrites the file. If you email yourself the original rather than the converted output, you will send the old cover.
The precise route: Sigil
Sigil edits EPUB source directly, so nothing else is touched. Use it when the book's formatting matters or when Calibre's result was not clean.
- Open the EPUB in Sigil.
- In Images, delete the old cover and add the new one, and give it the same filename if you want to skip the next two steps.
- Open the cover XHTML page and check the
imgsource points at your new file. - In Tools → Metadata Editor, confirm the cover reference.
- Save.
Keeping the filename identical is the shortcut: the existing references stay valid and only the pixels change.
Get the image right first
A cover that is technically embedded and visually wrong is no better. Before replacing anything:
| Check | Target |
|---|---|
| Aspect ratio | 1.6:1 tall, roughly 1600 × 2560 |
| Format | JPEG for photographic, PNG for flat art and text |
| File size | Under about 2 MB; large covers bloat the book |
| Legibility | Title readable at thumbnail size |
| Colour | RGB, not CMYK |
Store requirements differ and a cover that fits one can be cropped by another. Ebook cover sizes that work in every store has the specifics. A print edition is a different file again, with spine width and bleed to account for.
Why the old cover still shows
Four causes, in the order they usually apply:
Your reader cached it. Kindle, Apple Books and Calibre's own viewer all cache thumbnails. Remove the book from the device or app entirely, then re-add it. This is by far the most common cause and nothing is actually wrong with the file.
You saved the wrong copy. Calibre changed its library record; the file you then uploaded was the original. Convert or save to disk first.
Only one of the two places changed. The metadata points at the new image but the cover page still displays the old one, or the reverse.
The store has not reprocessed it. Amazon and other retailers cache covers for a period after an update. That one is waiting, not fixing. And if you are uploading a revision, what Amazon KDP wants from your file covers the rest of the upload.
If the file now refuses to validate after editing, why your EPUB was rejected and how to read EPUBCheck is the next stop.
The better version of this problem
Editing a cover inside a finished EPUB is repair work. It is necessary when the book is already built and the only copy you have is the output, but it is the slowest possible place to make the change, and it has to be repeated for the PDF.
bukpress takes a Markdown manuscript and exports both the typeset PDF and the reflowable EPUB from that one source, with the cover set once as part of the book rather than patched into a finished file afterwards. Changing it is changing one setting and rebuilding, and both formats come out matching, which is the same argument as EPUB or PDF, and why you probably want both.
That does not help with an EPUB someone else produced, which is exactly when Calibre is the right answer. The sample book shows what the output looks like, and from Markdown draft to published book covers the whole route.
Common questions
How do I change the cover of an EPUB?
Add it to Calibre, use Edit metadata to replace the cover image, then convert EPUB → EPUB or save to disk so the change is written into the file itself.
Can I edit an EPUB cover for free?
Yes. Calibre and Sigil are both free and both do it. Calibre is easier; Sigil is more precise.
Why does my EPUB still show the old cover?
Usually a cached thumbnail in your reader: delete and re-add the book. Otherwise you saved the original rather than the converted file, or only one of the two cover references was updated.
What size should an EPUB cover be?
About 1600 × 2560, a 1.6:1 tall ratio, in RGB and under roughly 2 MB. Check the title is readable at thumbnail size.
Does changing the cover break the EPUB?
It should not. Calibre's conversion rewrites the book, which can alter unusual formatting. Use Sigil if the interior is delicate, and run EPUBCheck afterwards either way.