The Internet is kind of awesome. This afternoon while in a taxi between customer sites I was thinking about the next print I want to do and how much filament it would need and that it shouldn’t be too hard to calculate the length of the filament left on a spool given it’s thickness and the inner and outer diameter of the spool.. sure enough someone has already written that calculator for you.
Direct link: https://jscalc.io/calc/1Cj6c1zxnr4q8Tzw