or click to choose. MOBI and PRC Kindle books work too.
Add a Kindle book to compress it. You’ll see how much smaller each picture gets, plus the book’s format and DRM status.
Compressed entirely in your browser. Your books are never uploaded.
This AZW3 compressor makes Kindle books smaller by resizing and re-saving their pictures, and by removing the copy of the source files that KindleGen leaves inside. It works with .azw3 (KF8) books and older .azw books, and leaves the text, layout, chapters and fonts exactly as they are. You can check every picture before and after and see what takes up space in each book. Everything runs in your browser and your books are never uploaded.
How to compress an AZW3 or AZW file
- Drop one or more
.azw3or.azwfiles onto the left box, or click it to choose them. - Each book is compressed right away. Results shows the savings and where they came from.
- Open Pictures to compare each picture’s size before and after, or Inside to see the book’s format, DRM status and what fills the file.
- Adjust the quality or resize setting if you want, and the books are redone automatically.
- Click Download. Several books download together as one ZIP.
Which Kindle files work
| File | What it is | Works here? |
|---|---|---|
.azw3 | KF8, the Kindle format made by KindleGen, Calibre and Kindle Previewer | Yes |
.azw (older books) | A MOBI book, usually with Amazon DRM | Yes. DRM books keep their DRM. |
.mobi, .prc | The original Kindle format, often with a KF8 book inside too | Yes |
.azw or .kfx from recent Kindle downloads | KFX, Amazon’s newest format, usually with DRM | No. These can only be opened by Kindle apps. |
Topaz .azw | An old scanned-page Kindle format | No |
If you drop a file that isn’t supported, the tool tells you what it is instead of producing a broken book.
Where the savings come from
- Pictures. Covers, photos, comic pages and charts are usually most of an AZW3 file. Each one is resized to fit the Kindle screen you pick and re-saved, and only replaced if the new version is smaller.
- KindleGen source. Books built with KindleGen carry a full copy of the original EPUB or HTML and a build log. Kindles never read them, so removing them changes nothing you can see.
- Not the text. Text is stored compressed already. It’s never changed, so links, footnotes, the table of contents and your reading position stay intact.
In KF8 books, PNG pictures stay PNG. The book’s text names each picture’s format, so changing PNG to JPEG could stop pictures from showing on some devices. PNGs are still resized when they’re bigger than the screen.
Picking a resize setting
| Setting | Good for |
|---|---|
| 2480 px | Kindle Scribe, and comics or manga you’ll zoom into |
| 1680 px | Kindle Paperwhite, Oasis and Colorsoft. The default. |
| 1448 px | Basic Kindle and older Paperwhites |
| 1024 px | Kindle apps on phones, or the smallest possible file |
The number is the longest side of each picture. A picture bigger than the screen only takes up space, because the Kindle shrinks it to fit anyway.
Is the compressed book safe to use?
A Kindle book is a table of numbered records, and pictures are linked by record number. The tool swaps picture records for smaller ones and rewrites the table, so everything else stays exactly where the book expects it. It then reads the new file from scratch, checks every record and opens every changed picture. A Checked tag means it passed. Keep the original until you’ve opened the new copy on your Kindle.
Frequently asked questions
Can this remove DRM or convert KFX?
No. DRM books keep their DRM, and KFX books can’t be read outside Kindle apps. If a DRM book has pictures the tool can read, they’re still shrunk, but only your Kindle can confirm the book still opens.
Why did my AZW3 barely shrink?
Books that are mostly text have little to gain, because their text is already compressed. Books made with Calibre don’t carry KindleGen source, so their savings come only from pictures. The Inside tab shows what each book is made of.
What does the Inside tab show?
The title, author, format (KF8, MOBI 6, or both in one file), text compression, DRM status, and how much of the file is text, pictures, fonts, KindleGen source and indexes, before and after.
Will the pictures look worse?
On e-ink screens, Balanced quality is very hard to tell apart from the original. For color screens and photo books, use High quality. Don’t resize keeps every picture at its original size and only re-saves the ones that come out smaller.
What are the HD pictures?
Some KindleGen books store a second, high-resolution copy of each picture for Kindle Fire tablets. They’re shrunk the same way, and they’re marked HD in the Pictures tab.
Are animated GIFs supported?
GIF pictures, animated or not, are left exactly as they are.