CHM to EPUB Converter

Convert CHM to EPUB online for free. Fast, secure, and high-quality conversion with no sign-up or software required.

Free to useNo file stored beyond 1 hourEncrypted over TLS 1.2/1.3No watermarks

or drag and drop files here

Maximum file size is 1GB

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How it works

Three steps to your converted file

Everything happens in your browser tab - upload, pick a format, download. The heavy lifting runs on our servers.

Upload your file

Drag and drop, click to browse, or paste a URL. Batches take up to 20 files at once - 230+ input formats across video, audio, image, document, and archive types.

Choose an output format

Pick from over a hundred output formats. Filter by category or search by name - every option is open to everyone, no account needed.

Convert & download

Hit Convert and grab your download link moments later. Originals are erased when the job completes; results are cleared within about an hour.

What is a CHM file?

The CHM (Compiled HTML Help) format is a proprietary binary documentation format developed by Microsoft for software help files. It encapsulates a collection of HTML pages, hyperlinks, and image assets into a single LZX-compressed archive, indexed via a binary table of contents (HHC) and keyword index (HHK). The format relies on the Information Tech Storage (ITS) file system structure, allowing for rapid random access and full-text search capabilities within the Windows Help environment.

How to open a CHM file

Windows operating systems provide native support via the built-in Microsoft HTML Help Executable (hh.exe). On macOS and Linux systems, which lack the proprietary Windows API, third-party viewers are necessary. KchmViewer is a standard solution for Linux/KDE environments, while xCHM provides cross-platform compatibility for macOS and BSD distributions.

CHM Technical Info

Full Name: Microsoft Compiled HTML Help
Developed By: Microsoft
Initial Release: 1997
MIME Type: application/vnd.ms-htmlhelp

What is an EPUB file?

EPUB (Electronic Publication) is an open e-book standard maintained by the World Wide Web Consortium (W3C), originally developed by the International Digital Publishing Forum (IDPF). It utilizes the Open Container Format (OCF) based on ZIP compression to package XHTML content, CSS styling, and XML metadata. EPUB supports reflowable content, allowing text to adapt to various screen sizes, and fixed-layout rendering for graphic-heavy publications. The current version, EPUB 3.2, supports HTML5, SVG, and JavaScript interactivity.

How to open an EPUB file

EPUB files require dedicated e-reader software as most operating systems do not natively render them. On desktop environments (Windows/macOS/Linux), Calibre is the industry-standard management tool, while Adobe Digital Editions handles DRM-protected files. For mobile devices, Apple Books (iOS) and Google Play Books (Android) provide native rendering. Browser-based extensions like EPUBReader for Chrome allow viewing without standalone software.

EPUB Technical Info

Full Name: Electronic Publication
Developed By: IDPF / W3C
Initial Release: 2007
MIME Type: application/epub+zip

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Why RunConvert

The fastest way to convert any file

Purpose-built for speed, privacy, and breadth of format support.

Convert CHM to EPUB in seconds

Every CHM to EPUB conversion runs on our servers, so your device stays fast and the output quality stays intact.

Fast, cloud-powered

No queue, no waiting. Files are processed on high-performance servers and returned in seconds, even for large files.

Secure & private

Encrypted in transit and never shared with anyone. Uploads are erased the moment your job completes, and results shortly after.

Free - no account needed

Convert without creating an account - no credit card, no trial clock. Sign in only if you want history and higher daily limits.

Developer API

Convert CHM to EPUB via API

Automate CHM to EPUB conversions in three steps: create a job, upload your file, then poll for the result.

# 1. Create job
curl -X POST https://api.runconvert.com/v3/jobs \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "tag": "chm-to-epub",
    "tasks": {
      "upload-file": {
        "operation": "import/upload"
      },
      "convert": {
        "operation": "convert",
        "input": "upload-file",
        "output_format": "epub"
      },
      "export-result": {
        "operation": "export/url",
        "input": "convert"
      }
    }
  }'

# 2. Upload your file (use upload_url from the response)
curl -X PUT "$UPLOAD_URL" --upload-file input.chm

# 3. Poll for result
curl https://api.runconvert.com/v3/jobs/$JOB_ID?include=tasks \
  -H "Authorization: Bearer YOUR_API_KEY"

Replace YOUR_API_KEY with your RunConvert API key. Get your free API key at runconvert.com/api.