How does Amazon Kindle count a standard page?
Or, if I may ask more specifically:
What is a believable range of character lengths for a standard page as calculated for Amazon Kindle?
It can estimate page and word counts for a given ebook, using various algorithms, and one of them is an APNX estimation based on Amazon Kindle.
You can try to use it and perform your own tests; if you have a decent amount of books, once it has counted the total words of each one and estimated the page numbers, you can do your math and calculate the average words per page.
This can be really hard to estimate without narrowing your question down a bit.
But I just measured a text-heavy book to determine:
Mobile Phone App 852 characters 26 lines
On a small e-ink device:
2003 characters 41 lines somewhat small font size
1666 characters 37 lines somewhat large font size
Users can adjust text margins and text size, so that plays a role. Also, my sample didn't have many paragraphs or line breaks. I was using a custom font on my large tablet, it seems that Bookerly is slightly smaller, so maybe add an extra 100.