A free space on an 8GB kindle is about 6GB and a typical book size (texts only) is about 1MB. This means you can store 6000 such books in an 8GB kindle. Some books may be larger than 1MB, but it still should be able to hold 2000 to 3000 books easily.
Correspondingly, does Kindle Paperwhite have SD card slot?
The Amazon Kindle Paperwhite e-reader does NOT have a micro SD card slot on the device. … If you want a micro SD card slot in a device, you can get any current line of Amazon Kindle Fire tablets that have a micro SD card in them: For the Amazon Fire 7 tablet, you can get a micro SD card up to 256 GB.