1Upload every file you want combined — at least two of them.
2Drag the uploaded items into the order you want; the order is taken from the list, not from the filenames.
3Start the merge, which joins matching inputs without re-encoding them and reconciles mismatched ones exactly once.
4Download the single combined EPUB file.
Merge EPUB FAQ
Is the merge lossless?
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It is whenever the inputs already agree — the encoded data is copied straight through. It stops being lossless only when the inputs disagree and something has to be re-encoded to make them compatible, and even then it is one pass, not one per file.
How does Merge EPUB join the files together?
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Concretely, the books are combined into one spine in the order you set, each source becoming a top-level section, and one table of contents is built over the result rather than several being concatenated. Upload everything you want combined and the result comes back as a single file.
Anything specific to EPUB when merging?
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Yes — the book is a zip of XHTML with a manifest, so the text costs almost nothing and every decision that matters is about the embedded images and font subsets. That is worth checking when the inputs did not all come from the same source.
How many files can I combine at once?
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On the free tier a merge accepts two files at a time, which is deliberately higher than the single-file limit on other tools because merging one file is meaningless. A pass removes the cap entirely.
Which eBook formats can I upload to Merge EPUB?
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EPUB is read natively, and MOBI, AZW3, FB2 and CBZ are accepted and normalised into the same internal representation first. The container is identified from its header, so a book renamed by a sync tool still opens.
Is there a file size limit on Merge EPUB?
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Yes: free accounts process eBooks up to 25 MB each, which is orders of magnitude above any normal novel; the OPF manifest, the spine order and the embedded fonts are handled by the same EPUB toolchain a desktop reader uses. A text-only book is a few hundred kilobytes, so the only files that approach the cap are illustrated ones — comics, cookbooks and textbooks with full-page artwork.
Will Merge EPUB damage the reflow or the table of contents?
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No. An eBook is XHTML plus a manifest, not a set of fixed pages, so the structure is edited as structure: the spine order, the NCX or NAV table of contents and the internal anchors are rewritten consistently rather than re-rendered.
Can I process several EPUB eBooks at once?
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Yes. A batch is queued in parallel with the same settings, which is the case that matters here — people arrive with a whole library rather than one book.
Why does a EPUB site host Merge EPUB?
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EPUB.to is built around the open eBook format — XHTML in a zip, reflowable by design, and readable on hardware nobody has thought about the layout for. A book is a zip full of markup, images and fonts, so almost every job people bring to an eBook site is really a job on one of those things. Merge EPUB runs on the same upload and the same account as the conversions because that is where it is needed.
What should I do with the result once Merge EPUB is finished?
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The converter on this site moves books between EPUB, MOBI, AZW3, PDF and DOCX, so a title ends up on whatever hardware is actually going to read it. Doing that after Merge EPUB means the conversion is made from the version you settled on, not from the one you were still fixing.
Is Merge EPUB here the same tool the sibling sites run?
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The engines are shared — the same toolchain, the same workers, the same limits. What a EPUB site adds is a view on reflow: which of these operations a reflowable book genuinely supports, and which ones only make sense on the fixed-layout media inside it. It also starts from one fact about the format this site is named after: the book is a zip of XHTML with a manifest, so the text costs almost nothing and every decision that matters is about the embedded images and font subsets.
Do I need an account, and does anything get kept?
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No account, and nothing is kept: uploads are deleted from the workers shortly after the job finishes, nothing is read and nothing is indexed. Free accounts exist for history and batch size, not for access.
