How do I know how wide the spine will be? There’s a simple formula which determines that width. Just take the number of pages in your book and divide that figure by your text paper’s PPI (Pages Per Inch). Where do you get the PPI? It depends on what kind of paper you’re using and it usually appears on the printer’s estimate or quote. If for some reason it doesn’t appear there, ask the printer for it. Let’s say your book has 200 pages and you are printing it on a web press using a paper which has a PPI of 400. Then the width of your book’s spine will be 200 ÷ 400 or half an inch. That’s for a paperback. For a hard cover book, you have to add the thickness of the boards. The easiest way to do this accurately is to have your printer provide you with a template.

Spine Width Calculator