I have my printer enclosed so I cannot easily see the spool to check how much filament is remaining - also lazy. After pondering a little bit I realized that it would be pretty simple to add a cheap load cell to the printer, put the spool on it when new then count backwards from 1000 grams to tell how much filament is left on the spool. A 5kg load cell with a HX711 amplifier board is under $10 on amazon. All the necessary libraries for python to utilize a HX711 are extant. It should be pretty easy to write an Octoprint plugin to add spool weight monitoring. I would do it except for two things - I don't know python, and I don't want to learn python.

Here is where the project is at: the spool holder is designed and works fine to hold a spool of filament. I have been printing off of it for a few weeks. All that is needed is software to interface the load cell to octoprint. I am tossing this up here, along with making a post on the octoprint forums in the hopes that someone with the necessary python skills will be interested enough in this existing to write the software then we can put it together into a plug in.

To put one together you will need a 5kg load cell and HX711 board. You will need m4 button head screws for the spool side and m5 screws for the bracket side. For now I have only designed a bracket for the stock ender style spool holder mount, if this gets off the ground I will design other styles as I am sure others will run with the idea too.