File Size Considerations | Vellum Help

File Size Considerations

Ebooks in Amazon’s mobi format are larger than equivalent EPUB files. The size of this file should not be used to estimate Amazon’s Delivery Costs, which are computed when you upload your file to KDP.

Kindle File Size

The size of a mobi file can be surprising, especially when compared to an equivalent EPUB file:

The mobi file is so much larger because it actually contains several files within: versions for each Kindle format (MOBI7, KF8), as well as an entire copy of the source EPUB file used to create it.

These multiple versions are created via Amazon’s KindleGen program, which Vellum uses to convert a file into Amazon’s proprietary mobi format.

Kindle Delivery Costs

Unique to Kindle is a Delivery cost that is based on the size of the ebook delivered to readers (applicable when selecting the 70% royalty option).

This calculation is not based on the size of the .mobi file generated via KindleGen. Rather, it is based on the smallest (MOBI7) component shown above.

To illustrate the difference, here are sizes and cost for a sample mobi file uploaded to KDP:

mobi size 2.4 MB
Delivery size 0.3 MB
Delivery cost $0.04

Note: Cost is based on the rate of $0.15/MB. See Amazon’s Pricing Page for details.

The only way to determine this delivery size is to upload your file to KDP. You’ll find the file size after conversion and resulting Delivery costs on the Kindle eBook Pricing page:

The KDP Dashboard reporst a file size after conversion of 0.3 MB

Fonts, Images, and Kindle Delivery Costs

As shown above, it is the smallest (MOBI7) version of your book that is used to compute Delivery Costs. This version:

This means that any high-resolution images or embedded fonts included in the KF8 version of your book will not affect your Delivery Costs.

Store Size Limits

Stores will not accept files larger than the following sizes:

Apple Books 2048 MB
Google Play 2048 MB
Amazon 650 MB
Kobo 100 MB
Barnes & Noble 20 MB

To acommodate these limits, Vellum may reduce images included in each version of an ebook, using high-resolution images where limits are high and low-resolution images where limits are low:

Resolution
Apple Books Very High
Google Play High
Kindle High
Kobo Medium
Nook Low
Generic EPUB Low

To satisfy the requirements of every store (including Barnes & Noble), Vellum’s Generic EPUB output also uses low-resolution images. For this reason, we recommend directly uploading store-specific ebooks when possible, especially when image quality is important.