KDP spine and cover calculator
The spine width of a KDP paperback is the page count multiplied by the thickness of one sheet: 0.002252 inch on white paper, 0.0025 on cream paper. Nothing is added.
The official formula
Cover width = bleed (3.2 mm) + back cover + spine + front cover + bleed. Height = book height + 2 × 3.2 mm. The page count is that of your interior PDF, rounded up to an even number, blank pages included.
Why calculators do not all give the same spine
Some add a 0.06-inch “safety” margin. KDP adds nothing: its own help page gives pages × thickness. A spine that is too wide lets the title spill onto the front cover; rely on the official formula and on the template downloaded from KDP.
You receive: the interior PDF ready to upload to KDP, the EPUB for the ebook, and the exact dimensions of your cover.