Ebook covers – 5x8 inches (1600x2400 pixels) at 72dpi
Paperback covers – 5x8 inches (full wrap: 10x16 inches with extra for bleed and spine) at 300dpi
Audiobook covers – 2400x2400 pixels at 72dpi
These are my default sizes and resolutions. They work perfectly for Amazon, Barnes and Noble, Kobo, Apple, Google Play, and others (this is what I use for my personal covers).
Let me know if you want a different size for your paperback. I’ll create the cover using your preferred size.