OVER-EXTRUSION (BLOBBY, OVERSIZED PRINTS)
Bumpy surfaces, oversized parts, walls that don't sit flat? Over-extrusion has four common causes. Diagnose flow rate, e-steps, filament diameter and temperature.
⚡ 10–30 minintermediatehigh confidenceover extrusionflowe-steps
Quick Fixes
Reset flow rate to 100% as baseline
Calibrate e-steps with 100 mm method
Measure filament diameter with calipers
Lower nozzle temp 5C
Run single-wall cube calibration
WHY THIS HAPPENS
Over-extrusion is the opposite of under-extrusion: the printer is delivering more plastic per millimetre of toolpath than the slicer commanded. The slicer calculates extrusion volume based on layer height, line width and filament diameter, then divides by filament cross-section to get mm of filament feed per mm of toolpath. If any of those calculations is wrong, the actual deposited volume diverges from intended.
The most common cause is flow rate (extrusion multiplier) set too high in the slicer. Users raise it to fix some other issue (layer adhesion, gaps), forget about it, then everything they print is over-extruded. The default is 100% (1.0 multiplier); above 100% means more plastic than the slicer thinks it needs.
E-steps and filament diameter are the same problem at different points in the calculation chain. If the slicer thinks filament is 1.75 mm but it actually measures 1.78 mm, the slicer underestimates volume per millimetre of feed and tells the extruder to push too much. If the extruder's e-steps setting is high (steps per mm too many), the motor pushes more filament per commanded millimetre than the firmware tracks. Both produce identical visible symptoms.
WHEN THESE FIXES FAIL
**If you recently raised flow rate to fix some other problem** - reset to 100% and re-test. Forgotten flow adjustments are the most common cause.
**If walls measure consistently 5-10% thicker than expected** - flow rate or e-steps off by that percentage. Calibrate.
**If only some prints are over-extruded** - per-filament flow setting in the profile. Check that filament's specific flow value.
**If you switched filament brands and over-extrusion appeared** - filament diameter changed. Measure with calipers.
**If over-extrusion only appears at high speeds** - probably not over-extrusion at all, probably temperature too high causing plastic to spread.
MOST LIKELY CAUSES
1
Flow rate too high
high confidence
Excess filament causes bulging, blobs, rough surfaces, and oversized walls.
→ Reset flow rate to 100% as a baseline
→ Lower flow in 2-3% steps after measuring a single-wall cube
→ Keep final flow in the 95-100% range unless calibration proves otherwise
2
E-steps not calibrated
high confidence
The extruder may push more filament than the firmware expects.
→ Calibrate e-steps with the 100 mm method
→ Save the new e-step value to firmware
→ Re-test extrusion until 100 mm commanded equals 100 mm moved
3
Filament diameter set incorrectly
medium confidence
If slicer diameter does not match actual filament diameter, extrusion volume is miscalculated.
→ Measure filament diameter with calipers in 4-5 spots
→ Enter the measured average diameter in the slicer
→ Run a single-wall cube calibration after updating diameter
WANT SETTINGS TUNED FOR THIS ISSUE?
Generate slicer settings based on your printer, filament, and this exact problem.
Generate SettingsWhat It Looks Like
Surfaces are bumpy or rough across the whole print, walls measure thicker than the model specifies, and layers don't sit flat on each other - the print looks bloated.
Why It Happens
Over-extrusion is the opposite of under-extrusion: the printer is delivering more plastic per millimetre of toolpath than the slicer commanded. The slicer calculates extrusion volume based on layer height, line width and filament diameter, then divides by filament cross-section to get mm of filament feed per mm of toolpath. If any of those calculations is wrong, the actual deposited volume diverges from intended.
The most common cause is flow rate (extrusion multiplier) set too high in the slicer. Users raise it to fix some other issue (layer adhesion, gaps), forget about it, then everything they print is over-extruded. The default is 100% (1.0 multiplier); above 100% means more plastic than the slicer thinks it needs.
E-steps and filament diameter are the same problem at different points in the calculation chain. If the slicer thinks filament is 1.75 mm but it actually measures 1.78 mm, the slicer underestimates volume per millimetre of feed and tells the extruder to push too much. If the extruder's e-steps setting is high (steps per mm too many), the motor pushes more filament per commanded millimetre than the firmware tracks. Both produce identical visible symptoms.
What The Community Data Says
Based on 55 confirmed fixes from r/FixMyPrint, these are the causes ranked by how often they actually worked:
1. Flow rate set too high - dropping from 105% or more to 95-100% fixed the most cases. Often left over from troubleshooting an unrelated issue.
2. E-steps not calibrated - calibrating extruder steps-per-mm corrected systematic over-feed, especially after any extruder hardware change.
3. Filament diameter wrong - measuring actual filament with calipers (often 1.78 mm vs slicer's default 1.75 mm) and entering true value fixed many cases.
4. Temperature too high - dropping 5-10C produced less-fluid plastic that spread less wide than over-fluid plastic at high temp.
5. Single-wall calibration not run - users who hadn't calibrated flow with the single-wall cube method discovered their setup was off by 5-10%.
Data sourced from r/FixMyPrint - one of the largest 3D printing troubleshooting communities on Reddit. This represents real user-reported issues and community-confirmed fixes, not theoretical advice.
How To Diagnose Your Specific Cause
If you recently raised flow rate to fix some other problem - reset to 100% and re-test. Forgotten flow adjustments are the most common cause.
If walls measure consistently 5-10% thicker than expected - flow rate or e-steps off by that percentage. Calibrate.
If only some prints are over-extruded - per-filament flow setting in the profile. Check that filament's specific flow value.
If you switched filament brands and over-extrusion appeared - filament diameter changed. Measure with calipers.
If over-extrusion only appears at high speeds - probably not over-extrusion at all, probably temperature too high causing plastic to spread.
Fixes By Cause
Cause 1: Reduce flow rate
Reset to 100% as a baseline. Drop in 2-3% steps (100% to 97% to 95%) while printing a single-wall cube and measuring wall thickness with calipers. Don't go below 90% without investigating root cause - flow correction is for fine tuning, not for compensating for major calibration errors.
Cause 2: Calibrate e-steps
Mark filament 100 mm from extruder inlet. Command 100 mm extrusion (heat hotend first). Measure actual feed. New e-steps = current x (100 / actual). For over-extrusion, actual > 100, e-steps should be reduced. Update firmware (Marlin: M92 E<value> then M500). Klipper: edit `rotation_distance`.
Cause 3: Measure and set filament diameter
Calipers on filament in 4-5 spots, average. Enter exact value (e.g., 1.74 or 1.77) in slicer's filament profile. '1.75 mm' filament commonly measures 1.70-1.80 mm. A 0.05 mm error = 6% volume error.
Cause 4: Lower nozzle temperature
Drop 5C and reprint. Cooler plastic spreads less, deposits cleaner-edged lines. Stay within filament's safe range - too cold causes layer separation.
Cause 5: Run single-wall calibration
Print a 0% infill, 1-perimeter, no-top/bottom cube. Measure wall thickness with calipers. New flow = current x (target_line_width / measured_wall). Repeat until measured equals target +/- 0.02 mm. Most well-tuned printers end at 96-100% flow.
Printer-Specific Notes
Bowden printers (Ender 3 family): Stock e-steps are usually within 5% of correct but drift over time as the extruder gear wears. Calibrate yearly. Plastic extruder lever is a common variable - replacing it requires re-calibration.
Direct drive printers (Bambu, Prusa MK4S): E-steps are factory-calibrated and usually accurate. Over-extrusion on these printers is more often filament diameter or flow rate setting than e-steps.
Enclosed printers (Bambu P1S, K1 Max): Higher chamber temperature can cause plastic to spread more than expected. Drop temp 5C below open-air values for cleaner extrusion.
Filament-Specific Notes
PLA / PLA+: Most consistent diameter across brands. Default 1.75 setting usually within 1% of true.
PETG: Diameter varies more between brands (1.70-1.80 typical). Always measure new spools with calipers.
ABS / ASA: Moderately consistent. Measure on first use of a new brand.
TPU: Often measures undersize (1.70-1.73). Counter-intuitively, this means the slicer over-estimates volume and you'll see under-extrusion not over-extrusion if you don't measure.
Specialty (PA, PC, fibres): Always measure. Composites and high-temp filaments often have inconsistent diameter.
How To Prevent It Next Time
Reset flow rate to 100% by default in every slicer profile. Adjust only after measuring with the single-wall calibration method.
Measure filament diameter on first use of any new spool. Takes 30 seconds with $5 calipers, prevents 6% volume errors.
Re-calibrate e-steps yearly and after any extruder hardware change. Drift is real and matters.
Get An Exact Fix For Your Setup
Use FixMyPrint to get flow rate, nozzle temperature and calibration check values tuned for your specific printer and filament - based on what actually worked for similar issues in the community.
Go to /settings-generator to generate yours.
Recommended Slicer Settings
Related Guides
Under-Extrusion (Gaps, Thin Walls, Missing Lines)
Gaps in walls, thin lines, missing infill - under-extrusion has five common causes. Diagnose which one applies to your print and fix only that one.
⚡ 15–45 minintermediatehigh confidenceunder extrusionclogs
Elephant Foot (Bulging First Layers)
Base of your print bulging out wider than the rest? That's elephant foot. Fix it with Z-offset, slicer compensation and first-layer temperature.
⚡ 5–10 minbeginnerhigh confidenceelephant footfirst layer
Blobs and Zits on Print Surfaces
Small bumps and pimples on the surface of your print are caused by pressure buildup at line starts and stops. Fix them with pressure advance, seam placement, wipe and coasting.
⚡ 15–30 minintermediatemedium confidenceblobszits
SKIP THE GUESSWORK
FixMyPrint generates exact settings for your specific printer, filament, and slicer - in seconds. No manual tuning required.
Generate My Fix