An older Kindle that doesn't take EPUB, or a Kindle workflow that's been using MOBI for years. EPUB is the modern target, but sometimes MOBI is what you actually need.
MOBI vs EPUB on Kindle
Amazon used MOBI (and later AZW3/KF8) as the Kindle's native format for over a decade. In 2022 Amazon added EPUB support to Send to Kindle. Older devices (pre-2018, roughly) may not handle EPUB well; for those, MOBI is the safer bet.
For a modern Kindle, both work. EPUB is generally cleaner because it's the open standard and converters target it first.
Conversion path
Convert via Flint's convert hub, pick MOBI. Side-load to your Kindle via USB, or email to your Kindle's @kindle.com address. The MOBI shows up in your library.
For email transfer, the attachment must be under 50MB. Larger PDFs need compression before conversion.
Same caveats as EPUB
Text-based PDFs convert cleanly. Scanned PDFs need OCR. Two-column journal layouts are unpredictable. Heavy design degrades. None of this is specific to MOBI; it applies to any PDF-to-ebook conversion.
Should you still use MOBI in 2025?
Only for older Kindle compatibility. For everything else, EPUB is the better choice — better tooling, broader future support, simpler workflow on modern Kindles. If you're not sure which your Kindle supports, try EPUB first.
FAQ
Is MOBI being deprecated?
By Amazon, gradually. The format still works but EPUB is the future direction.
Do all Kindles support MOBI?
Yes — every Kindle ever made supports MOBI. Old devices specifically may struggle with EPUB but always handle MOBI.
Can I email a MOBI to my Kindle?
Yes — to your @kindle.com address. Max attachment size is 50MB.
What's better quality?
Identical for text. MOBI and EPUB convert from the same source PDF and end up roughly equivalent.
Older Kindle workflows still work. Convert your PDF to MOBI when MOBI is what you need.