If you do a lot of 3d-prints, you know the problem, that you want to run a job, but you don't know, if you have enough filament loaded to the printer.
All the slicer's I know, add a comment line to the gCode-File, where they calculated the usage in meter or millimeter. But I usually order my filament in kilogramms.
To weight the loaded spool on the printer is a very easy way which is doable. Most time you have an empty spool from the same vendor. If you subtract the empty spool from the
weight of the loaded spool you get the weight of the filament.
To get from the weight of the filament to the lenght of the filament I built this little calculator.