7 Best Free Ebook Converters Online (Tested in 2026)
There are dozens of ebook converters online, but most are slow, strip formatting, or upload your files to unknown servers. We tested 7 of the most popular options to find which ones actually deliver on their promises.
What We Tested For
We evaluated each converter on five criteria that matter most to real users:
- Formatting preservation: Does the output retain bold text, italics, images, hyperlinks, and paragraph spacing?
- Speed: How quickly does the conversion complete for a typical 5 MB ebook?
- Privacy: Does the tool upload your file to a server, or does it process locally?
- Ease of use: Can you convert a file in under 30 seconds without creating an account?
- Format support: Which ebook formats are supported (EPUB, MOBI, PDF, AZW3, etc.)?
1. CheersPDF — Best for Privacy and Speed
Formats: EPUB ↔ PDF, MOBI → PDF, PDF → EPUB
CheersPDF is a browser-based converter that processes everything locally using JavaScript and Web Workers. Your files never leave your device — there’s no server upload at all. This makes it the most private option on this list by a wide margin.
Conversion is fast — a 5 MB EPUB converts to PDF in under 3 seconds on most devices. The output quality is excellent, with proper chapter breaks, embedded images, and clean typography. The PDF to EPUB converter preserves hyperlinks, font styling (bold, italic, monospace), image dimensions, and paragraph spacing.
Pros:
- 100% private — no file upload, no server, no account
- Fast conversion (under 5 seconds for most files)
- High-fidelity formatting preservation
- Works on any device with a modern browser
- supports files up to 100 MB for typical ebooks
- Completely free with no hidden upsells
Cons:
- Fewer format combinations than Calibre (no AZW3 or FB2 yet)
- No batch conversion (one file at a time)
Our pick: CheersPDF is the best choice if privacy matters to you, or if you want a fast, no-hassle conversion without installing software. Try the PDF to EPUB converter or the EPUB to PDF converter.
2. Calibre — Best for Power Users
Formats: Virtually all ebook formats (EPUB, MOBI, AZW3, PDF, FB2, LIT, PDB, and more)
Calibre is the gold standard of ebook management software. It’s a free, open-source desktop application that can convert between almost any ebook format, manage your library, edit metadata, and even serve ebooks over your network.
The conversion engine is powerful but complex. Getting good output from PDF to EPUB requires tweaking settings like heuristic processing, line unwrapping thresholds, and sometimes custom CSS. For straightforward EPUB to MOBI or EPUB to PDF conversions, the defaults work well.
Pros:
- Supports the widest range of formats
- Extensive customization and configuration options
- Built-in ebook library management
- Open source and completely free
- Local processing (no upload)
Cons:
- Requires installation (Windows, macOS, Linux)
- Steep learning curve for optimal results
- PDF conversion quality varies without manual tuning
- Interface feels dated
3. CloudConvert — Best Cloud-Based Option
Formats: EPUB, MOBI, AZW3, PDF, FB2, LRF, and more
CloudConvert is a well-established cloud conversion service that handles ebook formats alongside hundreds of other file types. It uses Calibre’s engine on the backend, which means conversion quality is generally solid for most format pairs.
Pros:
- Wide format support
- No installation required
- Good conversion quality for most formats
- API available for developers
Cons:
- Uploads your file to their servers (privacy concern)
- Free tier limited to 25 conversions per day
- Slower than local tools (upload + processing + download)
- Paid plans for higher usage
4. Zamzar — Simplest Interface
Formats: EPUB, MOBI, PDF, AZW3, FB2, and more
Zamzar has been around since 2006 and is one of the most recognizable names in online file conversion. The interface is dead simple: upload, choose format, convert, download. It supports a wide range of ebook formats.
Pros:
- Extremely simple to use
- No account required for basic conversions
- Been around for 20 years (reliable)
Cons:
- Files are uploaded to their servers
- Free tier limited to 2 files per day and 50 MB
- Conversion quality is average — formatting often degraded
- Slow processing for larger files
5. Online-Convert — Most Format Options
Formats: EPUB, MOBI, PDF, AZW3, FB2, LIT, LRF, PDB, and more
Online-Convert supports an impressive number of ebook format combinations. It also offers some customization options like target reader device, font size, and margin settings.
Pros:
- Lots of format options and customizations
- Can specify target device for optimization
- No account needed for basic use
Cons:
- Files uploaded to their servers
- Aggressive ads on the free tier
- 100 MB file size limit on free tier
- Conversion quality inconsistent across formats
6. Convertio — Clean Interface with Cloud Processing
Formats: EPUB, MOBI, PDF, AZW3, FB2, and more
Convertio offers a clean, modern interface with drag-and-drop file upload. Like CloudConvert, it processes files on their servers. The free tier allows up to 100 MB files and 10 conversions per day.
Pros:
- Clean, modern interface
- Good selection of ebook formats
- Optional Google Drive / Dropbox integration
Cons:
- Files uploaded to remote servers
- 10 conversions per day on free tier
- 100 MB file size limit
- Formatting preservation is inconsistent
7. To EPUB — Dedicated EPUB Converter
Formats: PDF, MOBI, AZW, DOC, and various formats to EPUB
To EPUB (toepub.com) is a specialized converter focused exclusively on converting other formats to EPUB. It’s simple and single-purpose, which some users prefer over multi-format tools.
Pros:
- Focused on EPUB output
- Simple, no-frills interface
- Free to use
Cons:
- Files uploaded to servers
- Only converts TO EPUB (not from EPUB)
- Limited formatting control
- Quality varies depending on source format
The Bottom Line
For most users in 2026, two tools stand out:
- CheersPDF if you want speed, privacy, and zero installation. It’s the only converter on this list that never uploads your files. Perfect for quick EPUB/MOBI/PDF conversions.
- Calibre if you need maximum format support and don’t mind installing software. It’s the most powerful tool available, but requires more effort to get optimal results.
If privacy isn’t a concern and you need a quick cloud-based conversion, CloudConvert is the best of the upload-based options with solid quality and a reasonable free tier.
Try CheersPDF — The Private Ebook Converter
Free, private, and instant. No sign-up required.