EPUB → HTML

What is EPUB?

EPUB is the open e-book standard maintained by the International Digital Publishing Forum. Technically it is a ZIP archive holding XHTML content, CSS, images and an OPF manifest that defines reading order. Its defining trait is that it reflows: content and presentation are separate, so a reader re-lays-out the text for the current screen and font size. That is why one file looks right on a phone, a tablet and a desktop, and why EPUB is the most portable format outside the Kindle ecosystem.

What is HTML?

HTML / XHTML is the structural language of the web and is literally the content format inside an EPUB; .mhtml (MHTML) packs a page together with all its resources (images, CSS) into one file, which is what "save as a single page" produces. XML is the general markup language that formats such as FB2 and OPF are themselves written in. The whole family is tagged text where the tags carry the structure, so how much structure survives a conversion depends on how well the tool understands them.

What to watch out for when converting EPUB to HTML

Extracting from the source

EPUB content is XHTML fragments plus separate CSS. Extraction must follow the OPF manifest's spine for reading order and its toc for navigation. Concatenating files in ZIP name order — the most common mistake when flattening an EPUB to a single TXT — scrambles the chapters.

Writing the target format

Whether images and styles are linked or embedded decides if the result travels as one file. To ship a single file, inline the assets as data URIs or use MHTML; otherwise moving the file breaks the images. Keep semantic tags (h1–h6, p) so a later EPUB conversion still yields a table of contents.

Where the two formats interact

• The source carries real navigation while the target has no concept of chapters, so reading becomes one long scroll. If navigation still matters, keep explicit, uniformly formatted chapter heading lines in the output.
• Flattening a structured archive into one text file requires ordering chapters by the manifest (spine), not by ZIP entry name. This is the easiest mistake to make and the hardest to notice: the file opens fine, but the chapters are shuffled.

Post-conversion checklist

1. Convert the first three chapters as a trial and check for lost text, interleaved lines or misplaced blocks before doing the whole book.
2. Jump to five random spots and search a character name to confirm the text is fully searchable.
3. Confirm illustration count and placement — check that images are not all dumped at the end of a chapter.
4. Fill in title, author and language — a wrong language tag breaks typesetting such as Chinese line breaking.

Converting novels: what is different

Fiction is the most common and the most peculiar kind of e-book: hundreds or thousands of chapters, almost no figures, often nothing but a TXT source, and Chinese sources that frequently carry anti-piracy garbling. These are the points that bite hardest.

• A long novel can run to hundreds or thousands of chapters, so the table of contents decides whether the result is usable. Normalise chapter headings to one recognisable pattern first — say "Chapter N Title" alone on its own line — or the target will miss chapters, merge them, or collapse the whole book into one.
• Volume markers ("Volume One", "Volume Two") usually degrade to ordinary headings, losing the volume/chapter hierarchy. If that matters, promote volume headings one level in an editor afterwards so they are not siblings of chapter titles.

Tools for converting EPUB to HTML

Any of the tools below can handle this direction; pick one by your operating system and how many files you have. Read the previous section first — doing the steps out of order (converting a scanned file before running OCR, for instance) usually means starting over.

Common questions

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