The Right File Sizes for Kindle Books

Amazon's Kindle platform was designed, in part, to remove some of the technical barriers to entry into the self-publishing market. As such, Amazon sets only one rule about the size of an ebook: The total file can't exceed 50 megabytes in size.

Ebooks in General

An ebook is a supplier-agnostic platform, which means that any ebook that meets the EPUB3 standard should work on any reader. The EPUB3 framework does not mandate minimum or maximum file sizes for an ebook, but ebooks that transfer privately—like versions sold by an author through his own website—probably ought to be optimally sized.

Ebooks on Kindle

Amazon doesn't use the EPUB3 standard, however. Instead, the company converts ebooks into a proprietary Kindle ebook format, and it's these Kindle-optimized versions that sell on Amazon's website and push to Kindle devices. For Kindle ebooks, Amazon specifies a limit of 50 MB for the total size of the file.

Optimizing Ebook Size

The text of an ebook contributes very little to the overall file size. Because, under the hood, an EPUB3 file is a glorified web page, there's little you can do to make a text-based ebook smaller.

However, size grows with two things.

First, the cover—which ought to be large enough to display nicely on various-sized displays—requires minimum dimensions that promote larger file sizes. Amazon ebook covers should be 2,500 pixels tall by 1,563 pixels wide, although Amazon will accept them as small as 1,000-pixels-by-625-pixels. Aim for a file that's 300 dots per inch or pixels per inch; Amazon doesn't require it, but it's precise enough to look good if it's printed. The file may be a JPG or TIF file.

Amazon imposes a reimbursement penalty if the file size of the cover image exceeds 2 MB.

The other consideration relates to images inside the book, in line with the text. Every image consumes some extra file size. Optimizing those images by making them grayscale or converting them to line art helps. There's little cause for a high-resolution interior image unless you're creating an art book—and art books aren't an optimal choice for ebook conversion.