Line width setting in your slicer — usually equals nozzle diameter
Your current extrusion multiplier / flow setting
Measure at 4–5 points around the cube and average them

How to print the test cube: Use a single-perimeter, 0% infill cube (20mm × 20mm, any height). Disable top/bottom layers if possible. Use the same temperature and speed as your normal prints. Let it cool fully before measuring.

↗ Get Flow Cube STL
Corrected Flow Rate
%