Flow Rate

Theory

Flow rate (often called extrusion multiplier) compensates for differences between actual and assumed filament diameter, extruder step calibration, and material compressibility. At 100% the printer extrudes exactly the calculated volume. Above 100% produces over-extrusion (raised ridges, poor dimensional accuracy); below 100% causes under-extrusion (gaps between perimeters, weak infill). Volumetric flow rate (mm3/s) is a hardware limit set by hotend melt capacity and nozzle diameter.

Application

Calibrate flow rate per filament spool using a single-wall cube test. Measure wall thickness with a calliper; adjust flow rate until measured width matches the extrusion width. Typical values: 95-105%. Separately calibrate pressure advance (Klipper) to compensate for pressure-related flow variation at corners and speed changes.

Common mistakes

Adjusting flow rate to compensate for under-extrusion caused by a partial clog masks the real problem: clear the clog instead. Flow rate interacts with print speed: at high speeds the hotend cannot melt filament fast enough regardless of flow multiplier setting. Different filament colours from the same brand can require 1-3% flow adjustment due to pigment filler content variations.

Related terms: Extrusion Width, Print Speed, Nozzle