Make more money on Kindle by reducing your .mobi file size

Make more money on Kindle by reducing your .mobi file size

I made ebooks for a client recently – the ebooks came out at 15mb. I’ve never paid much attention to file size, but she pointed out that, if you are participating in Amazon’s 70% royalty option, they charge a fee per MB every time your book is downloaded – right now in the US it’s $0.15 per MB.

Check the Amazon pricing page for the most up-to-date prices and costs.

At 15mb she would be paying $2.25 per sale!

So she wanted me to make them smaller….

Step One: Clean up the Code

First I went through and got rid of any extra code I code remove, and made sure it passed the epub checker here:

(I’m using Sigil to edit the epub before converting to mobi).

That got it down to about 7mb, which still wasn’t good enough – $1.05.

Step Two: Reduce the Image Resolution

Kindle Fire HD will display 1200width… so you need images that big, but they don’t need to be perfect quality. Instead of “maximum” you can probably save them at “High” or about 60% quality…. people aren’t going to spend much time looking at your cover on your Kindle anyway, and it usually won’t be displayed full screen – ever.

They see it in the book shelf, click on it and it goes to about half screen size… to see it bigger they have to open the book and then scroll back to the very beginning of the book.

It was mostly the cover image, which I resized to about half – there’s also the logo, the dividers and the author photo I could have shaved down a bit.

The file is now 2.7mb – but that’s still a 40cent fee – if you’re selling books for $1.99 that’s about half your profit!

Step Three: Get Rid of Embedded Fonts

I took the same mobi file and ran it through Calibre, saving from mobi to mobi: the resulting file is only 794 KB.

It isn’t very pretty, but it looks fine and simple. You don’t really need the special fonts matching the print book, most ebooks don’t have them (probably for just this reason).



I just checked my own KDP account and found the following:

One of my mobi files was 15mb – but after uploading it to Kindle it’s only 2.6mb – the delivery cost is $0.39.

The other was 4mb, but after uploading it’s only .7mb and costs $0.11.

The other is 7mb and it’s about the same

And these are big ebook files with loads of pictures and embedded fonts.

No wonder I never paid attention to file size before.

Should you worry about it?

Not too much. Whether you’re making your own mobi files or uploading a Word file for conversion, it’s probably going to end up pretty small.

On the other hand, you can earn more money by making your files smaller.

If you sell 1000 books, that 11cent charge is $11o – and the 40cent charge is $400!

Calibre is probably the best way to make small files… but then you can’t edit them if their are problems with the mobi. I tried exporting from Calibre to epub, then editing the .7mb file in Sigil, then converting with Kindle previewer, but it went back up to about 2.2mb (which KDP will probably bring back down to .7mb again or less).

It’s more important to be clean, and to work, and not be ugly. Especially in the beginning when you’re making first impressions.

So don’t tear your hair out. But once you’re selling 1000 a week, you can hire someone on to figure this out for you and save some extra cash.


  • Diane Challenor Posted

    What a great post. Thanks for the info re file size. And, most importantly, thanks for your generousity.

  • S. J. Pajonas Posted

    All great ideas. Yeah, Amazon compresses files when it gets them which saves some hassle. My mobi file for my last book which had a big map image in it was 1.9mb and Amazon crunched it down to 0.7mb for a delivery fee of $0.12. I believe that Scrivener outputs really clean files with no extra code. I’ve been pretty happy with their compiler!

    • Diane Challenor Posted

      SJ Pajonas, I’m relieved to hear you’ve found Scrivener’s compiler OK. I’ve recenlty read about formatting and was starting to worry about the time involved gettig the formatting right. Currently I use Scrivener to create an eBook from which I proof read and highlight problems. I convert the author’s text from a Word document by cut and pasting into Scrivener and then converting the text into an eBook to be read on my Kindle. it worked so well, problem free, I felt confident that the file would be nice and “clean” for publishing on Amanzon. And then, my confidence was “rattled” completely when I read about the formatting traps. So thank you for sharing your experience. I feel better now!

      • S. J. Pajonas Posted

        Diane, Scrivener’s compile formatting is definitely a little rough to get used to the first time through, but once you learn all the ins and out, you can save your settings and use them over and over again. I just learned a little trick about compiling and adding in a prologue at the beginning! I didn’t want the prologue labeled as “Chapter One” and I found a neat setting that allowed me to skip it. I’ve been using Scrivener for almost 3 years now and I learn something new and awesome almost every day 🙂 The compiled files always come out clean and compact. I’m very happy with it.

        • Diane Challenor Posted

          Thank you! Best wishes for your work.

  • Rob in Ohio Posted

    Hi Derek… Rob from 52 Novels here. I suspect Sigil uses kindlegen to make Mobi files from the epub output. If this is the case, then the packaged Mobi has as many three versions of the book: a KF8-ready version (if those features were used) for Kindle devices and apps that can play them, a version for legacy Kindle devices and apps, and also the source epub. This results in a final file size that’s as much as three times the size of the source epub.

    As you’ve noted, however, the reported delivery size is smaller. Amazon isn’t compressing the file (kindlegen does that already), but rather it’s displaying the file size as if a single version was inside the Mobi package and calculating the delivery charge accordingly.

    In the case of your 15 MB file that reports as 3 MB… kindlegen makes some allowances for hi-res images, maintaining the originals and creating lo-res versions for the legacy version. Without taking a peek inside the Mobi, I can only speculate, though.

    All that said, DIYers should continue to be aware the things you mentioned in the post. But it’s okay if they see a simple novel come in at 350 kb for the epub and +1 MB for the Mobi.

    • Derek Murphy Posted

      Hi Rob, Sigil doesn’t save to mobi but I was using Kindle previewer to generate mobi files, so you’re probably right about the multiple formats – that’s really interesting.

      • Rob in Ohio Posted

        Kindle Previewer has Kinglegen inside it, so, yep.

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