This explains where to find the KDP cover template generator for one piece paperback covers to be used in Photoshop, GIMP, Illustrator, etc. (not how to upload separate jpgs to the Cover Creator). After entering some basic information, a template will be generated with the correct dimensions, having calculated for the bleed and spine width.
Enter your trim size (the finished size of your book) from the pull down menu. Next, enter the page count for the entire number of pages in your document, including all front and back matter. Your word processing program will have a page count (in LibreOffice it’s in the bottom left of the Writer application). Or, if you’ve already exported to PDF, your previewer or Adobe reader will tell you how many pages. Enter the total page count. Finally, enter the type of paper you want for your book’s interior. Creme is heavier than white and will affect the width of the spine. Once all your info is entered, click the yellow Download cover template button.
The template generates immediately and downloads as a zip file. Open that and you’ll find two files in your folder, a PDF and a PNG file. You can open either one in Photoshop, Illustrator, or other program to create your cover.
When you set-up your title on KDP, make sure your trim size, page count, and paper color are the same as you entered for your cover template. If the information doesn’t match, you’ll most likely receive an error.