Inksky
Not all ebook formats are created equal. Here’s what you need to know.
Quick Comparison
| Feature | EPUB | MOBI/AZW3 | |
|---|---|---|---|
| Reflowable | ✅ Yes | ✅ Yes | ❌ No |
| Font adjustment | ✅ Yes | ✅ Yes | ❌ No (fixed) |
| Images | ✅ Yes | ✅ Yes | ✅ High quality |
| DRM | Adobe DRM | Amazon DRM | Various |
| Kobo support | ✅ Native | ❌ No | ✅ Basic |
| Kindle support | ✅ (via Send) | ✅ Native | ✅ Basic |
| BOOX support | ✅ Native | ✅ Via app | ✅ Excellent |
EPUB — The Universal Standard
Best for: Most readers, most devices
EPUB is the industry standard format (except for Kindle). It’s reflowable, supports adjustable fonts, and works natively on Kobo, BOOX, PocketBook, and most other e-readers.
Pros:
- Reflowable text — adapts to any screen size
- Adjustable fonts, line spacing, margins
- Open standard (no vendor lock-in)
- Works with libraries (OverDrive/Libby)
Cons:
- Not natively supported on Kindle (but Send-to-Kindle works)
MOBI/AZW3 — Amazon’s Legacy
Best for: Older Kindles
MOBI is Amazon’s legacy format. Newer Kindles actually use AZW3/KFX, but all are commonly called “MOBI.”
Pros:
- Native on all Kindles
- Supports Amazon’s Whispersync
- Good for Kindle-exclusive content
Cons:
- Doesn’t work on Kobo, PocketBook
- Older format (being phased out)
- Less flexible than EPUB
PDF — For Print-Ready Documents
Best for: Fixed-layout documents, academic papers
Pros:
- Exact layout preservation
- Works on any device
- Good for text-heavy academic papers
Cons:
- Doesn’t reflow (hard to read on small screens)
- No font size adjustment
- Large file sizes
Which Should You Use?
| Situation | Best Format |
|---|---|
| Reading on Kindle | EPUB (via Send-to-Kindle) or AZW3 |
| Reading on Kobo / BOOX / PocketBook | EPUB |
| Library books | EPUB (OverDrive/Libby) |
| Academic PDFs | PDF (on large screen) or PDF |
| Archiving | EPUB (open standard) |
Real-world decisions
“I bought a book on Google Play Books — can I read it on my Kindle?” Possibly, but it depends on DRM. Google Play exports EPUBs with Adobe DRM, which Kindles don’t support. You’ll need to use Adobe Digital Editions to download the file, remove the DRM (for personal use, where legally permitted), and then send the cleaned EPUB to your Kindle.
“Should I convert my EPUB library to AZW3 for long-term storage?” No. EPUB is an open standard maintained by the W3C and will be readable for decades. AZW3 is Amazon’s proprietary format, and while it works today, there’s no guarantee a non-Amazon reader will open it in 2035. Keep masters in EPUB, convert to AZW3 as needed for your Kindle.
“Why does my PDF look terrible on my Paperwhite but fine on my Scribe?” PDFs don’t reflow, so on a 6-inch screen your full-page document is shrunk to fit, making text microscopic. The Scribe’s 10-inch screen can display an A4/Letter page at roughly 70% of its original size, which is readable. If you regularly read PDFs, screen size is the single biggest factor — format conversion can’t fully fix the problem.
The format you don’t need anymore
MOBI was the Kindle standard for over a decade, but Amazon announced in 2022 that Send-to-Kindle would phase out MOBI support. Today, MOBI files sent through the service still work, but they lack newer Kindle features like custom fonts and enhanced typesetting. If you’re converting books today, skip MOBI entirely — use AZW3 for direct USB sideloading or EPUB for Send-to-Kindle.