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Dial In Your Extrusion Multiplier With One Test Print

· 2 min read 3d-printingcalibrationextrusionflow-rate

Extrusion multiplier (flow rate) scales how much plastic the extruder pushes for a commanded length. Wrong values show up as gaps between perimeter walls (under-extrusion) or bulging top surfaces and dimensional error (over-extrusion). Every spool deserves its own value.

What you need

  • Digital calipers reading to 0.01 mm
  • A thin-wall calibration model, such as a hollow single-wall cube or a flow-tower test
  • The slicer profile where you set per-filament flow
  • A ruler to measure actual filament diameter

Step by step

  1. Measure your filament diameter at several points along the spool with calipers. Enter the average into the slicer. Cheap PLA often measures 1.73 mm, not 1.75, which alone skews flow by over a percent.
  2. Set the extrusion multiplier to its default, typically 0.95-1.00 for direct drive.
  3. Slice a model with at least two vertical perimeter walls and no infill near the outer surface, then print it.
  4. Let the part cool fully on the plate. Warm walls measure thinner than they really are.
  5. Measure the outer wall thickness at mid-height with calipers: jaws lightly touching, not clamped. Take readings from four sides and average them.
  6. Divide the measured thickness by the programmed wall line width. For example, 0.40 mm programmed walls measuring 0.37 mm gives 0.925.
  7. Multiply your current multiplier by that ratio and update the filament profile. If you started at 1.00, enter 0.93.
  8. Reprint the same model and remeasure. One iteration gets most filaments within 2%; a second nails it.
  9. Record the final number in the slicer profile name or notes so it survives filament swaps.

Common mistakes

  • Compensating for a clogged or partially blocked hotend by cranking flow; fix the hardware first, see [[unclog-3d-printer-nozzle]].
  • Measuring squishy PETG walls immediately off the build plate while still soft.
  • Confusing extrusion multiplier with esteps calibration; both matter, and linear advance interacts with flow at speed changes.

Related guides

Flow tuning pairs naturally with first-layer work described in [[3d-printer-bed-leveling-first-layer]], since both control how plastic meets the plate. Once walls come out dimensionally accurate, push print speed intelligently using the tradeoffs in [[slicer-speed-vs-strength]].

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