How to Add a Cover Image to Your EPUB

Every reader app — Apple Books, Google Play Books, Kindle, Kobo — shows a cover thumbnail in the library. No cover means a grey placeholder. Here's what you need to know to get it right the first time.

Image specs that actually matter

Format: JPEG or PNG only. The EPUB spec allows more, but GIF and WebP break in enough readers to avoid them.

Dimensions: 1600 × 2560 px is the safe target — Amazon's Kindle standard, and sharp on modern e-ink and tablet screens. Hard minimum is 625 × 1000 px; below that, Apple Books renders it blurry.

Aspect ratio: 1:1.6 portrait. Square or landscape covers look wrong in library grids everywhere.

File size: Under 2MB for the image. A 4MB cover can push a lean EPUB over Kindle's 50MB email limit. If you're already over, compress the EPUB after adding the cover.

Colour space: RGB. CMYK images silently break in most reading apps.

Adding a cover with Epublys

1. Open the metadata editor
2. Upload your EPUB — existing cover and metadata load automatically
3. Under Cover Image, select your JPEG or PNG
4. Save and download

The editor updates the OPF manifest correctly — which is the step that most manual attempts miss. Free tier: EPUBs up to 10MB. Pro handles up to 100MB.

Why a cover can exist in the file but not display

This is almost always an OPF problem. Three common causes:

• The image was dropped into the ZIP without updating the manifest — the reader never finds it
• The OPF has a <meta name="cover"> entry pointing to an ID that doesn't match any item in the manifest
• EPUB 2 vs EPUB 3 mismatch — some readers look for the cover in the <guide> element, others in the <manifest> cover property

Run the file through the EPUB validator — it checks manifest completeness and flags broken references with exact line numbers.

Other tools

Calibre: Right-click the book → Edit metadata → click the cover thumbnail → Browse. Works fine, but requires a desktop install and more clicks.

Sigil: Add the image to the Images folder, then manually set the cover property in the OPF. Only worth it if you're already in Sigil editing the book's HTML.

After adding the cover

• Validate — confirms OPF manifest and guide entries are correct
• Check other metadata — title, author, and language should be set while you're already in the editor
• Send to Kindle — the cover appears on the home screen after delivery

Related

• What is an EPUB file? — how the OPF manifest works
• Compress EPUB — reduce file size if the cover made it too large
• All free EPUB tools