Flow Calibration

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 change flow on real parts.

When flow calibration is worth your time

Calibrate flow when you see a consistent bias: walls always print too thick or too thin, top surfaces always have gaps or always look overfilled, or holes/slots are consistently off after first-layer and temperature are already reasonable. Recalibrate after switching filament type/brand, changing nozzle size, or making a major hotend change. Don’t use flow to hide problems like a partial clog, wet filament, a slipping drive gear, unstable hotend temperature, or a wrong nozzle diameter set in the slicer.

Before you print the test (lock the variables down)

• Confirm the slicer’s nozzle diameter matches your installed nozzle.
• Confirm filament diameter (1.75 vs 2.85); if available, enter an average from several caliper checks.
• Dry the filament if you see popping, steam, or bubbles.
• Start with a clean nozzle and reliable extrusion (no gear grinding or intermittent slip).
• Pick one nozzle temperature and keep it fixed through the whole calibration.
• Use your normal layer height, line width, speed, and cooling for that material; flow won’t transfer across wildly different settings.

Pick the right test: a single-wall coupon

Use a model that prints exactly one perimeter, with no infill and no extra walls (often called a single-wall or vase-style coupon). That makes your caliper reading map directly to the slicer’s intended line width. Skip multi-wall cubes for the measurement step—wall overlap, corner slowdowns, and infill/wall interactions can mask flow errors.

Measure and adjust flow (then confirm with one reprint)

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

Reading the result: what it usually points to

• Wall measures thicker than target and features look rounded/overfilled: flow is high, or temperature is high.
• Wall measures thinner than target with gaps and weak top layers/layer bonding: flow is low, or you’re too cold, partially clogged, or slipping at the extruder.
• Thickness varies a lot around the print: usually not flow; look for inconsistent filament diameter, intermittent feed slip, a nozzle obstruction, temperature swings, or mechanical drag.

Verify on real geometry (the coupon is not the finish line)

Once the single-wall thickness matches the target, print a small real part with 2+ walls and some top layers (for example a small open box). You want top surfaces that close without gaps and without raised ridges, clean seams, and improved hole/slot accuracy. Save the final flow per filament and nozzle size, and note the temperature, because flow can shift across materials and hotend setups.