As you probably know, Kindle cover images for the Amazon product catalog can be much larger in both dimensions and file-size than the cover that appears inside the book. The latest Kindle Publishing Guidelines spell it out.
Interestingly, verbiage about the “shortest side” (formerly a minimum of 500px) has been dropped in favor of simplified instructions about the longest side and the ratio of width to height.
Amazon has repeated the information in today’s Kindle Direct Publishing Newsletter. Here’s the scoop:
Our new guidelines for cover images require that an image be at least 1,000 pixels on the longest side, though we recommend 2,500 pixels on the longest side to ensure better quality, and an ideal height/width ratio of 1.6. To confirm whether your cover image meets these requirements, right-click the image file and select “Properties.”
The new directive means that the images I’ve been using, at 938×1250 or 900×1200, are a little puny compared to what is now encouraged. Do the math:
The smallest cover permitted for the Kindle catalog is now 625 by 1000 pixels.
The new recommended size is now 1563 x 2500 pixels.
Verify at Amazon KDP: Creating a Catalog/Cover Image: Dimensions
Note that a width of 1562.5 pixels would give you a precise 1.6 aspect ratio, but half a pixel doesn’t work very well. Now that they’ve specified a rounded-up width of 1563 pixels, just go along with it.
Remember that the pixel dimensions are what counts, not the resolution. A pixel is a pixel on the web. It’s only when you’re creating a cover for print media that resolution matters, so that the image prints at the right size and required resolution.
Have fun with this and keep the inside cover at 600×800 pixels, which is not a ratio of 1.6, but about 1.3. This means that you might have a little extra room on the catalog cover if you change the proportions. Note that the ratio of 1.6 is not a requirement. If you want to stick with the same ratio as the inside cover, that’s alright. Start with the bigger cover and reduce it instead of the other way around.