Walls are too thick, layer lines bulge outward, the surface looks rough and lumpy, or the print is dimensionally oversized. Material squeezes out from between layers and builds up on the nozzle.
Confirm It’s Over-Extrusion, Not Something Else
Blobs and surface roughness also appear with stringing, Z-seam issues, or wet filament. The specific sign of over-extrusion is walls that are measurably thicker than they should be and layers that squeeze into each other rather than sitting flat.
Print a single-wall vase (one perimeter, vase mode, 0.4mm extrusion width). Measure the wall with calipers. If it measures 0.48mm or more, you’re over-extruding. If it measures 0.40–0.44mm, the problem is elsewhere.
Calibrate E-Steps Before Adjusting Flow Rate
These are two different settings controlling different things. E-steps (steps/mm) controls how much the motor rotates per commanded millimeter. Flow rate (extrusion multiplier) is a percentage adjustment on top of that.
The correct order: calibrate e-steps first with a direct extrusion test, then use flow rate for fine-tuning only.
E-steps calibration: Mark the filament 100mm and 120mm above the extruder entry. Command 100mm of extrusion through the console (heat nozzle first, use G1 E100 F300). Measure where the 100mm mark ended up. If the 100mm mark moved 97mm instead of 100mm, new_steps = old_steps × (100/97). Write the new value to EEPROM (M503/M500 on Marlin) and test again.
Adjust Flow Rate for Fine-Tuning
After e-steps are correct, print the single-wall vase test again. If the wall still measures over your extrusion width, reduce flow rate (extrusion multiplier) by 2% increments. Most properly calibrated printers run between 95–103% flow depending on material and hotend. If you need to go below 90% to get correct dimensions, your e-steps need recalibration, not flow rate adjustment.
Check Filament Diameter
The slicer assumes 1.75mm or 2.85mm — make sure it matches your filament. More importantly, measure your actual filament at 5 points along 1 meter of filament with calipers. Budget filaments sometimes vary ±0.1mm, which causes over/under-extrusion that changes as the print runs. If filament measures consistently 1.68mm instead of 1.75mm, set the filament diameter in the slicer to match.
Temperature Is Rarely the Cause
High temperature reduces viscosity but doesn’t add extra filament — the same volume is extruded regardless of temperature. Don’t drop temperature to fix over-extrusion. It’ll make layer adhesion worse without fixing the root cause.