Amazon's Kindle ecosystem has two legacy formats — **AZW3** (Kindle Format 8) and **MOBI** — and choosing between them matters if you want your book to look right. AZW3 keeps fonts, layout, and images. MOBI strips most of that away. This guide explains the difference so you can convert to the right format and avoid a broken file.
Quick comparison
| Feature | AZW3 | MOBI |
|---|---|---|
| Also known as | Kindle Format 8 (KF8) | Mobipocket |
| Introduced | 2011 | ~2000 |
| Embedded fonts | ✅ Yes | ❌ No |
| CSS styling | ✅ Full | ❌ Minimal |
| Images | ✅ Preserved | ⚠️ Often downgraded |
| Chapter structure | ✅ Good | ⚠️ Depends on source |
| Device support | Kindles 2011+ | Kindles ~2007–2015 |
| Amazon preference | ✅ Recommended | ⚠️ Legacy only |
Bottom line: AZW3 is the better format whenever your device supports it. For a detailed comparison including FB2 and Lit ecosystem notes, see FB2 vs EPUB and Lit format conversion guide. And if you need help diagnosing conversion issues after switching formats, our ebook troubleshooting guide covers the most common headaches.
What is AZW3?
AZW3 (Kindle Format 8) was introduced by Amazon in 2011 as the successor to MOBI. It is based on the EPUB standard but wrapped in an Amazon-specific container.
What AZW3 gives you:
- Embedded custom fonts — your chosen typeface survives.
- CSS3 styling — margins, spacing, and text decoration are preserved.
- Better image handling — covers and illustrations stay sharp.
- Chapter navigation — proper TOC and section breaks.
AZW3 is the recommended format for all Kindles released from roughly 2012 onward, including Paperwhite, Oasis, and basic Kindle models.
What is MOBI?
MOBI (Mobipocket format) is the original Kindle format, dating back to Amazon's acquisition of Mobipocket in 2005. It is still supported on older Kindles but is considered legacy.
What MOBI gives you:
- Simple, forgiving structure — works even with poorly formatted source files.
- Small file size — less overhead from missing advanced features.
- Universal Kindle compatibility — reads on every Kindle ever made.
What MOBI does not give you:
- Custom font embedding (limited to Kindle's built-in fonts).
- Advanced CSS or complex layout.
- Reliable image preservation for SVG or high-resolution graphics.
MOBI is only worth using if your Kindle is too old to support AZW3.
Which should you convert to?
Use this decision tree:
1. What Kindle do you have?
- Kindle Paperwhite (any generation), Oasis, Voyage, Kindle (2016+) → AZW3
- Kindle (2007–2015), Kindle Keyboard, Kindle 3 → MOBI (AZW3 may not work)
- Kindle Scribe, Kindle Colorsoft → AZW3
2. Where did the file come from?
- EPUB source → Convert to AZW3 for modern Kindles, MOBI for old ones.
- MOBI source already → Leave it; it will open on any Kindle.
- AZW3 source already → Leave it; it will open on most Kindles from 2011+.
3. Do you care about formatting quality?
- Yes → Always use AZW3. The difference in font and image preservation is significant.
- No → MOBI is fine for text-only novels.
Recommendation: Unless your Kindle is from before 2016, convert to AZW3. The better formatting is worth the extra step.
How to convert EPUB to AZW3 or MOBI
Both conversions are free and run in your browser with BookConv:
- EPUB → AZW3: /convert/epub-to-azw3 — recommended for all Kindles from 2016+
- EPUB → MOBI: /convert/epub-to-mobi — only for very old Kindles
- MOBI → AZW3: /convert/mobi-to-azw3 — upgrade your legacy files
- AZW3 → MOBI: /convert/azw3-to-mobi — downgrade for older devices
Files are deleted within one hour. No software installation required.
For a detailed comparison of these formats, see our AZW3 vs MOBI guide. If you need to convert from other sources like EPUB, check our EPUB to AZW3 conversion guide. Other format pairs worth knowing: FB2 to EPUB keep formatting, Lit to EPUB keep formatting, and Cbr to PDF guide for comic archives.