When we measure a book, it’s the inside page dimensions we are referring to (NOT the outer hardcover dimensions). So if we are discussing an 8.5 x 11″ hardcover, the actual outer dimensions of the book are 8.75″ x 11.25″ . See the digaram below for further explanation.
Here is an example of a hardcover template diagram for an 8.5″ w x 11″h page size book with the minimum spine thickness (0.375″). This spine size covers most children’s books and yearbooks of smaller page counts. As a book gets thicker in page count ( beyond the 0.375″ thickness, we can advise an exact spine size based on which type of paper is selected and the final page count. We have a “caliper sheet” below with a formula on spine width calculations. If ever any question, please contact firstname.lastname@example.org
Formula for Calculating Spine Width
Example: 200 pages text on 100 lb Silk text
Take the number of pages divided by 2: 100/2 = 100
Then multiply by the paper thickness: 100 x 0.0058 = 0.58″
and add .125” : 0.58 + 0.125