Some of the most common questions I get about building Kindle books regards file sizes: what is the right size for a Kindle book? What's the maximum size for a cover image? How big should internal images be? The answer to all of these questions really is “it depends.” It depends upon the length of your book, the number of images, and who you are targeting your book at.
Size of Your Books
Amazon estimates the average size of a Kindle book to be around 2KB per page, including the cover image and any internal images. But before you panic thinking that your book is much larger than that, there are some things to consider:
- This number is an average, and it is used primrily by Amazon to give estimates as to how many books a given Kindle ereader can hold. In other words, it's a marketing number.
- This number is also not a requirement or even a recommendation. Some books will be larger and others smaller, it's just the nature of books.
- Amazon also assumes that most of their books are going to be fiction, without a lot of internal images. But your readers will expect books with a lot of images to be larger than all-text books.
In fact, the only recommendation that Amazon provides is for authors using the KDP (Kindle Direct Publishing) tool. Amazon says “The maximum file size for conversion through Amazon KDP is 50MB.” If you create a book that is larger than 50MB it may not convert to KDP or it may cause delays in conversion.
Ebooks are Not Web Pages
If you've been building web pages for any amount of time, then you are probably very aware of file sizes and download speeds. This is because web pages need to be kept as small as possible to keep download times low. If a customer clicks on a link to a web page and it takes more than 20–30 seconds to download, most people will simply hit the back button and not return to the site.
This is not the same with ebooks. It's easy to think that ebooks will have the same effect, especially if you started by building your ebook in HTML. But this is incorrect. When a customer purchases an ebook, it is delivered to their ebook reader over the internet. The larger the file size, the longer it will take a book to download to the device. But even if it takes an hour for the book to load onto the device, it will be there eventually, even if the customer has long forgotten that they bought it. When the customer returns to their device library, they will see your book right there.
Most customers won't ever notice how long it takes a book to download. But you should be aware that some customers will notice and a long load time might be reflected in their review after they finish reading it. But on the other hand, if the book has lots of pictures they might expect a longer download time.
What About Images?
There are two types of images associated with Kindle books: images inside the book and the cover image. File sizes for these two types of images are very different.
Internal Images Images inside the book are the most common reason a Kindle book might be extremely large. There is no Amazon-specific recommendation for how large your internal images should be. I recommend using JPG images that are no more than 127KB each, but even this is just a guideline. If you need internal images to be larger, then make them larger. But remember that large images make your entire book larger, and take longer to download.
Cover Images Amazon's recommendation for cover images is “For best quality, your image would be 1563 pixels on the shortest side and 2500 pixels on the longest side.” They don't say anything about file size. Like with the book itself, there are probably file sizes that won't upload to KDP, but that size is certainly similar to the 50MB total file size. And if you cannot create a cover image that is smaller than 50MB (heck, even 2MB!) then you might be in the wrong business.
The Last Thing to Consider—The Kindle Devices Themselves
You might be thinking “but what if my book is too big to fit?” The reality is that this isn't going to be a problem. Kindle devices come with 2GB (or more) of on-device storage, and while not all of that is available for books, about 60% or more is. Even if your book is 49.9MB that is still significantly smaller than even the smallest device can hold.
Yes, it is possible that your customer will have already downloaded and installed thousands of books and thus not have room for yours, but no customer will blame you for their hoarding tendencies. In fact, they probably already know they have too many books on their device even if yours fits without a problem.
Don't Worry Too Much About File Sizes for Your Kindle Books
If you are selling your book on Amazon, then you shouldn't worry too much about how large your Kindle books are. They will download in the background and your customers will have the book eventually. Smaller is better, but your books and images should be the size that is right for your book and no smaller.
The only time you might worry about the file size is if you are participating in the Amazon 70% royalty option. With that option, Amazon charges a fee per MB every time your book is downloaded. The current cost in the U.S. is $0.15 per MB, and there are other rates for sales in other countries/languages. Check the Amazon pricing page for the most up-to-date prices and costs.