Flow Rate

Theoretical Background

What is Flow Rate (Extrusion Multiplier)?

In Fused Deposition Modeling (FDM), the Flow Rate (also referred to as Extrusion Multiplier or Flow Ratio in OrcaSlicer) is a scaling factor that controls the volume of filament extruded relative to the slicer's theoretical calculations. It acts as a fine-tuning coefficient applied to the extruder motor steps. While the printer's extruder calibration (E-steps) ensures that feeding 100mm of filament physically draws exactly 100mm into the extruder, the Flow Ratio adjusts for material-specific volumetric behaviors during extrusion.

Volumetric Flow Rate Conservation

The slicer translates a 3D model into a series of toolpaths with a specific cross-sectional area. The basic physics of extrusion is governed by the conservation of volumetric flow rate ($Q$): $$Q=A\times v$$ Where: