IS THERE A STANDARD EBOOK COVER SIZE THAT WORKS FOR ALL?
Yes, but note that different authors and designers have different preferences as there is no single recommended size as you can see from the size specifications by different sites. One important aspect is to study the topselling books in your specific genre and decide which dimension will fit in with the majority of the topselling books – do they look a little skinny (1.6 dimension), a little more wide (1.5 dimension) or very wide (1.33 dimension). Non-fiction books are often much wider too.
I tend to make my original files very large since I need to accommodate paperback editions of covers too, and those need a much larger size. Then I downscale from there. My standard proportions for fiction is 1.5 (6×9) as that is what the majority of topseling authors use.
I have been watching the Best Sellers Lists and Hot New Releases Lists in Amazon to see what sizes of covers are the most popular. To find these just use Google search and type in “Best Sellers in Paranormal Romance” or “Hot New Releases in Paranormal Romance” and replace Paranormal Romance with your own genre. It is a good idea to also study the style and type of covers used in your genre and theme.
Personally I make my covers 3200 x 4800 pixels and then make smaller versions for different sites. Half the size i.e. 1600 x 2400 works on all major sites, provided the file is less then 2MB in size as Barnes & Noble for example will not accept a file if it is bigger. The same original large file of 3200 x 4800 can be used to add a spine and back for a paperback version, provided the dpi is 300 – more info on that here: http://bookcoverscre8tive.com/paperback-book-covers/
The original file of 3200 x 4800 can be used for Amazon KDP also, though there is no hard-and-fast rule and Amazon will accept a minimum size of 1000 pixels in length, so you could make the cover smaller if you wish. However, Amazon keeps changing its policies and increasing size, so it is best in my opinion NOT to go smaller than half of the 3200 x 4800 size = i.e. 1600. x 2400.
My size works and there are books in the Top 100s in various categories in ebook stores with my covers. There may be other sizes though and different authors and designers have their own preferences. For non-fiction books a wider size is often quite popular.
For a run-through of different size specifications for different ebook sites, please refer to the Size Specifications Page.