Quick Verdict
Use AZW3 when…
Use AZW3 for new Kindle e-books — it supports modern layout features and is what Kindle Direct Publishing now requires.
Use MOBI when…
Use MOBI only for compatibility with very old Kindle devices (Kindle 1, Kindle 2, DX) or as an interchange format with older Kindle apps.
AZW3 vs MOBI: Feature Comparison
| Feature | AZW3 | MOBI |
|---|---|---|
| Format generation | 2011+ (KF8) | 1990s–2000s (Mobipocket) |
| Custom fonts | Yes | Limited |
| Drop caps | Yes | No |
| CSS3 support | Most features | Very limited |
| Kindle device support | Kindle 4+ (2011+) | All Kindle devices |
| Amazon submissions | Required for new books | No longer accepted (since 2022) |
When AZW3 wins
- ✓Format generation: 2011+ (KF8)
- ✓Custom fonts: Yes
- ✓Drop caps: Yes
When MOBI wins
- ✓Format generation: 1990s–2000s (Mobipocket)
- ✓Custom fonts: Limited
- ✓Drop caps: No
Frequently asked questions
Should I convert MOBI to AZW3?
If you're reading on a modern Kindle (Paperwhite, Oasis, or recent), AZW3 will give you better typography and layout. For older Kindles, MOBI works fine. Calibre converts both directions.
Are AZW3 files larger than MOBI?
Slightly — AZW3 supports more features and embeds custom fonts when used. For a 100,000-word novel, AZW3 might be 2 MB and MOBI 1.5 MB. Negligible difference for download or storage.
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More comparisons
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