How to Merge EPUB Files

To combine EPUB books into one ebook, use an online EPUB merger or Calibre's EpubMerge plugin. Both produce a new book with one reading order and table of contents. Calibre's separate Merge book records action combines library records and formats; it does not join the chapters of two EPUB files.

Method 1: Merge EPUBs online with Epublys

1. Open the Merge EPUB tool.
2. Add your DRM-free EPUB files. Free allows up to 10 files, 5MB per file and 20MB in total.
3. Drag the file cards into reading order. The first book supplies the default title and language.
4. Choose a title and author if you want to override the defaults, and choose whether to insert divider pages between books.
5. Click Merge EPUBs and download the combined EPUB.

The free website allows 3 tool operations per day. Pro removes the daily cap and allows up to 50 files, with 30MB in total per merge. All selected files must fit within the total limit; the file count does not multiply that allowance.

Your files are sent over HTTPS to a Cloudflare Worker, processed in memory, and returned without persistent file storage. If you need a fully local desktop workflow or your books exceed those limits, use the plugin method below.

Method 2: Calibre with the EpubMerge plugin

EpubMerge is a Calibre plugin that combines EPUB contents, including the source tables of contents. Install it through Preferences → Plugins → Get new plugins, search for EpubMerge, install it, and restart Calibre.

1. Add the DRM-free EPUBs to your Calibre library.
2. Select the books and choose the EpubMerge action from its toolbar button or menu.
3. Check the order in the merge dialog and set the combined book's metadata.
4. Complete the merge, then use Save to disk to export the new EPUB.

This is useful when you already manage the books in Calibre or need local processing. The built-in record merge is for duplicate library entries, so it is not a substitute for this plugin. See the Calibre comparison for editing and library-management differences.

Method 3: Run EpubMerge from the command line

With Calibre and the EpubMerge plugin installed, the plugin also exposes a command-line entry point:

calibre-debug --run-plugin EpubMerge -- -o combined.epub book1.epub book2.epub book3.epub

Use --title and --author to set the combined metadata. --flatten-toc flattens the navigation; --keep-meta retains the original metadata files for the plugin's unmerge feature. Run calibre-debug --run-plugin EpubMerge -- --help for the options in your installed version.

Check the result with EPUBCheck before publishing. A merge tool and a structural first-pass validator do not replace a full EPUB conformance check or a visual preview.

What Epublys keeps and changes

Title, author and identifier

Unless you enter a new title, the output uses the first book's title with (Merged) appended. Authors from all source books are combined unless you supply an author override. The language comes from the first book, and the output gets a new identifier. It does not copy every source metadata field: update publisher, description, subjects or series afterwards with the metadata editor.

Free output includes an Epublys publisher entry and colophon. Pro output omits that branding. A cover from the first contributing source with a declared cover is kept as the combined cover; replace it if you are making a new omnibus edition.

Chapters and table of contents

Source chapters stay in their reading order. The merged navigation groups each book under its title and carries over available source navigation. Optional divider pages separate the books. Preview the result and check that every intended chapter appears, especially if a source book had a missing or incomplete TOC.

Styles, images and fonts

Each source's asset paths and manifest IDs are renamed with a book-specific prefix, and file references are rewritten. CSS files are kept; their selectors are not rewritten into a new design. Fonts and images from different books remain separate copies, even when their bytes are identical. This avoids filename collisions but can make an omnibus larger than expected.

Different source books can still look different. If you need one consistent design, edit the combined styles in Sigil or Calibre's book editor. Use the compression guide to inspect oversized images and unused assets before reducing the file.

Check the merged EPUB before sharing it

1. Open it in a reader and follow the TOC through each source book.
2. Confirm title, authors, language and cover describe the combined work.
3. Run the structural validator for a first pass and EPUBCheck for full conformance before distribution.
4. If validation reports duplicate manifest IDs, missing files or malformed XHTML, repair those in an EPUB editor. Auto-fix only handles mimetype repairs and a missing language; it does not rename arbitrary IDs or recreate missing content.

IDs in different XHTML chapter documents can have the same spelling. A duplicate within one document, or duplicate IDs within the OPF manifest, is a different problem. Do not rename chapter anchors across the whole book without updating the links that refer to them.

Combining selected chapters instead of whole books

Extract a chapter range from each source first, then merge those range EPUBs in the order you want. The splitter returns one EPUB when you enter a chapter range; without a range it returns a ZIP of individual chapter EPUBs. Unzip that bundle before adding chapters to the merger.

• Edit EPUB metadata after making an omnibus.
• Compress a large EPUB when embedded assets dominate its size.
• Calibre and browser tools for other EPUB tasks.