Forget about RPM, thats from the old days when we used DC motors on the extruder. With stepper driven extruders we command a given length of extrusion, which is simpler and gives better quality than the old method of setting an extruder speed and moving the head to keep up with that.
The E codes in the gcode tell the extruder how much to extrude. All you need to do is calibration your E steps per mm so that when commanded to extrude 1mm of filament, the extruder takes in 1mm of filament.
The E codes in the gcode tell the extruder how much to extrude. All you need to do is calibration your E steps per mm so that when commanded to extrude 1mm of filament, the extruder takes in 1mm of filament.