This online calculator tool will help you arrive at the dimensions your full cover needs to be for Amazon KDP or you can just use it to figure your spine width. Different printers use different paper, which determines the spine width, which is why this calculator is specific to Amazon KDP.
1. For the “interior” parameter, you MUST enter either BW or Color. It will not work if you misspell them or put in any other text.
2. For the “paper color” parameter, you MUST enter either white or cream. It will not work if you misspell them or put in any other text.
3. If you are printing in color, then you HAVE to select white.
Instructional Video on How to Create and Export a Book Cover in Adobe Indesign
This video will show you how to set up and export a book cover in Adobe InDesign. I don’t recommend Photoshop for book cover compilation because that is not the right tool for the job. For starters, you are unable to individually manage or export each page of the cover (front, spine, back, dustjacket flaps, etc.). Second, Photoshop tends to export a more bloated PDF than InDesign.