The purpose of this web app is to provide a cover designer with guidelines on limits for text on the spine. Note: This is not a spine width calculator. Instead, it provides guidelines on how much text you can put on the spine.
You simply input the page count and it calculate the text size in inches & mm for both cream and white paper options (the author will need to specify one or the other).
NOTE: Spine text is only supported on books over 100 pages. Text on larger spines must be sized to fit the spine, with at least 0.0625" (1.6 mm) of space between the text and the edge of the spine.
If you want to double check the calcs, here are two resources:
You can view the live page of this repo here.
~ Brian