"Requirements for the size of your cover art have an ideal height/width ration of 1.6, this means:
• A minimum of 625 pixels on the shortest side and 1000 pixels on the longest side
• For best quality, your image would be 1563 pixels on the shortest side and 2500 pixels on the longest side
I just looked into an Amazon sample that had a cover 860 x 1226 px. The ratio is 1.426. So anything goes?
As for GraciousMe, who said in another thread she doesn't publish at Amazon, a cover with a size of 800 x 1000 px would be ok, though it has not the ideal ratio of 1.6 recommended by Amazon."
Thanks this has been useful as I've been playing around trying to get a better cover on a Kindle Paperwhite.
I started, following advice from elsewhere, with 600x800, ok but noticeably shorter than Amazon covers. I went up to 800x1280 as a ratio of 1.6 based on your post and other info. This is now the same height as Amazon covers but looks a little thin, being picky here.
So, I would suggest a near perfect rendition would be 960x1280 which at 1.33333 is yet another ratio.
Worth repeating though that I've only tried this on a Paperwhite.