In working with InDesign for a few recent projects, I’ve been trying to learn to use points and picas instead of inches. It’s more accurate and is the printing industry standard.
First, I changed my preferences to use points/picas instead. I thought I’d eventually get the hang of sizes. Alas, it’s not altogether different than learning metric after living with English measurements. My current project is a “half-size” non-fiction book (5.5″ x 8″). After placing the text, some fonts showed up 2 lines per page they were so large. So, I’ve gone back to my old ways.
So, today I searched for definitions and found this handy conversion chart. I hope you also find it helpful.