The basic formula for this measurement is stated as page count of the book divided by PPI (pages per inch).
If you have ever searched for information on calculating spine bulk, you have undoubtedly found that this formula should be used as a guide and there are other factors which can cause your book to be wider than anticipated.
When paper is manufactured, the mill that makes it will give each sheet a PPI rating. Many mills also include an allowance where a stack of paper could have a higher PPI than was stated.
This simply means the paper could be thicker or thinner. This allowance typically isn’t much however even small variations can have a dramatic impact on cover design. For example if there are lines and/or other graphics that fall outside of the type area, they can be pushed over the edge of the spine onto the front or back of the book.
Most small variances go unnoticed but if you have an exact spine design pay close attention to PPI and allowances set by the paper manufacturer. Your printer should have this information readily available.
Extras and Binding
In many cases, it isn’t just the pages and the cover that make up the final width of a book. Items such as photographs printed on thicker paper, inserts, supplemental material or bound-in CD’s can increase the thickness of a book substantially.
The bind style of your books can also affect the thickness. For instance RepKover or lay-flat binding can cause more thickness than traditional perfect binding. If the design of your cover is heavily dependent on thickness of the finished product, make sure your printer gives you an accurate picture of how all elements will affect spine bulk.
While spine bulk calculators, formulas or a template for a book cover can be a good guide, you should always work with a knowledgeable customer service rep to ensure your specifications are met.
What challenges have you faced with cover design and the width of your book? Has spine bulk ever been an issue?