Flow Calibration

Flow calibration sets your extrusion multiplier so the printer deposits the amount of plastic your slicer assumes for a specific filament, nozzle, and temperature. The practical method is: print a single-wall test at stable conditions, measure the wall thickness, adjust flow by ratio (target/measured), then confirm with a second print and a small real-world part.

TL;DR

Print a single-wall test, measure the wall thickness on straight sections, then set Flow (extrusion multiplier) to currentFlow × (target line width ÷ measured thickness). Reprint once to confirm before you “fix” real parts with flow.

A quick visual map of what to check first, how to measure, and when flow is not the right fix.

When flow calibration is worth doing

Calibrate flow when you see consistent, repeatable extrusion bias: walls always measure too thick or too thin, top surfaces show persistent gaps or persistent overfill, or holes/slots are consistently off even after basic first-layer and temperature are reasonable. Recalibrate after changing filament type/brand, nozzle size, or a major hotend change. Don’t use flow to “cover up” a partial clog, wet filament, a slipping drive gear, unstable hotend temperature, or an incorrect nozzle diameter setting in the slicer.

Before you print the test (stabilize the variables)

  • Slicer nozzle diameter is correct (wrong value ruins the target thickness).
  • Filament diameter is correct (1.75 vs 2.85); if your slicer allows, enter an average from a few caliper measurements.
  • Filament is dry enough for the material (popping/steam/bubbles = dry it first).
  • Nozzle is clean; extruder gear tension is correct (no grinding, no intermittent slipping).
  • Pick one nozzle temperature and keep it constant for the whole calibration.
  • Use your typical layer height, line width, speed, and cooling for that material (flow is not universal across wildly different settings).

Test choice: single-wall coupon (best for measuring)

Use a model that produces exactly one perimeter with no infill and no extra walls (often called a single-wall or vase-style coupon). This isolates extrusion width/thickness so your caliper reading maps directly to the slicer’s intended line width. Avoid multi-wall cubes for the measurement step because wall overlap, corner slowdowns, and infill/wall interactions can hide flow errors.

Measure and adjust flow (repeat once)

  1. Slice the single-wall model with a known line width (for example 0.45 mm) and 1 perimeter, 0% infill, 0 top layers.
  2. Print at steady speed and with normal cooling for the filament.
  3. Let it cool, then measure wall thickness in several straight sections (avoid corners and the first/last few millimeters). Average the readings.
  4. Compute new flow: newFlow = currentFlow × (targetWallThickness ÷ measuredWallThickness).
  5. Update the flow/extrusion multiplier in your slicer or filament profile and reprint the same test to confirm the wall matches the target.

Reading the results: what the symptoms usually mean

  • Measured wall thicker than target, rounded details, “elephant-skin” or overfilled look: flow too high (or temperature too high).
  • Measured wall thinner than target, gaps between adjacent lines, weak top layers and poor layer bonding: flow too low (or too cold, partial clog, slipping extruder).
  • Thickness varies a lot around the part: usually not a flow problem; suspect inconsistent filament diameter, intermittent feed slip, nozzle obstruction, temperature swings, or mechanical drag.

Verify on a real geometry (don’t stop at the coupon)

After the single-wall thickness matches the slicer target, print a small functional sample with 2+ walls and some top layers (for example a small open box). Look for: top surfaces closing without gaps and without raised ridges, clean wall seams, and more accurate holes/slots. Save the final flow value per filament and nozzle size (and note the temperature), since flow can shift between materials and hotend setups.