How can I calculate volumetric speed for Slic3r auto speed?



I have noticed that Slic3r offers a speed setting called "auto speed" meant to give a constant filament pressure at the extruder, which I believe could eliminate filament grinding issues at higher printing speeds.

According to the tooltip in Slic3r, auto speed is calculated from two parameters:

  • Maximum speed
  • Maximum volumetric speed

Maximum speed speaks for itself, but how can I calculate the maximum volumetric speed of my print?

Tormod Haugene

Posted 2016-01-13T17:57:10.633

Reputation: 3 919



Auto speed is calculated from maximum volumetric speed in mm3 per second. If you normally print at 80 mm/s, your extrusion width is 0.5 mm and you are printing 0.2mm high layers, your volumetric speed would be 80 * 0.5 * 0.2 = 8 mm3/s, which is the volume of plastic extruded by your printer every second when printing at that speed (not accounting for any die swell).

Ian Williams

Posted 2016-01-13T17:57:10.633

Reputation: 116

You are right about the terms: I have updated the post to reflect this. I also found a blog post discussing the math in context of extrusion width, for those interested:

– Tormod Haugene – 2016-01-14T20:36:23.890

Technically not an answer... he asked for the maximum one, you gave him how to calculate the "usual one" he already tested. – FarO – 2018-04-09T08:53:19.290


There's no fixed maximum volumetric speed that works for everyone, there's simply too much variables to account for. By using @Ian Williams explanation you can convert from volumetric to regular speeds but you still need to test what speed works best for your setup.

Just a few of the other variables affecting how fast material can come out consistently: temperature (nozzle & heat brake), extruder motor power, path friction between extruder and hotend, material compressibility, fluidity and glass transition temperature, ..

There are interesting topics on RepRap forums, like this one:,654085


Posted 2016-01-13T17:57:10.633

Reputation: 121