A print cover wraps the whole book: back, spine and front, plus bleed. Its size depends on the trim, the paper (cream paper is a little thicker than white) and the page count.
What you need: the trim, the paper and the interior's page count.
What you get: the spine width and the full cover size in inches and millimetres, the range of pages KDP prints for that binding, and whether the spine can carry text (from 79 pages).
The studio's cover editor builds the whole wrap from your own artwork at exactly this size.