How to Fix Under-Extrusion: The Settings (and Order) That Actually Work

Under-extrusion is one of the most common — and most misdiagnosed — FDM problems. It happens when your printer doesn’t push enough filament to fill the layers it’s been told to lay down, leaving thin, weak walls, visible gaps between perimeters, and a rough, patchy surface. The good news: it’s rarely a sign of a serious hardware fault. The bad news: it has a long list of possible causes, which is exactly why people burn an afternoon changing random sliders. This guide gives you the right way to fix under-extrusion settings — in the correct order, with concrete values you can act on today.

If you’d rather just upload a photo of the failure and get back exact slicer settings, that’s what our Diagnose tool is built for. But if you want to understand and fix it yourself, read on.

How to spot under-extrusion (and rule out other faults)

Before you touch a single setting, confirm you’re actually looking at under-extrusion. The classic signs are:

Thin, weak walls that flex or split along layer lines
Visible gaps between adjacent extrusion lines, especially on top layers
Sparse, broken extrusion that doesn’t fully fill the perimeter

A quick, reliable test: print a small calibration cube and hold one wall up to a bright light. If you can see pinholes or gaps between the lines, you’re under-extruding and likely need a marginal flow increase. If you’re not sure whether you’re chasing under-extrusion or something else entirely, our broader guide on why prints fail and the defect identification tool will help you name the defect before you fix it.

Fix it in the right order — or get misleading results

This is the part most tutorials get wrong. Calibrating in the wrong sequence gives you numbers that look right but don’t hold up. Work through it like this:

Rule out mechanical issues first. If your printer was fine yesterday and under-extrudes today, your E-steps didn’t magically change. The cause is mechanical — a partially clogged nozzle, heat creep, or a worn/slipping extruder. Calibrating software values to mask a mechanical fault is a band-aid that will fail again. Fix the hardware, then calibrate.
E-steps next. Get extruder steps-per-mm within 1–2% of correct. This is a firmware setting calibrated once per extruder.
Temperature before flow. Flow is highly sensitive to temperature, so run a temperature tower and lock in your ideal nozzle temp before you calibrate flow. Calibrate flow at the wrong temperature and every later number is wrong too.
Flow rate / extrusion multiplier last, calibrated per filament.

E-steps: fixing under-extrusion at the source

E-steps tells the printer how many motor steps equal 1 mm of filament movement. If that number is off, every print under-extrudes (gaps, weak parts) or over-extrudes (blobs) regardless of slicer tweaks. Many Creality machines ship at 93 steps/mm, which is commonly slightly off — treat that as a typical default to check, not a universal truth.

To calibrate:

Heat the nozzle to printing temperature (e.g. 200 °C for PLA). Cold extrusion gives false readings.
Load filament and mark it exactly 120 mm from where it enters the extruder body.
Send M83 (relative extrusion), then G1 E100 F100 to extrude 100 mm slowly.
Measure the remaining distance to your mark. If the printer didn’t pull exactly 100 mm, recalculate and update your E-steps, then save.

The distinction matters: E-steps is a firmware setting that accounts for your extruder hardware. Flow rate is a per-filament slicer setting that accounts for filament diameter variation and material behaviour. They are not interchangeable.

Temperature: the most common easy fix

A nozzle that’s too cool can’t melt filament fast enough to push the required volume — a classic, easily-resolved cause of under-extrusion. Adjust in 5 to 10 °C steps and watch the result. As rough reference ranges (always check the specific filament’s spec sheet): PLA typically prints at 180–220 °C and ABS at 230–250 °C.

One thing makers often miss: nozzle material changes the numbers. Hardened steel nozzles don’t retain heat as well as brass, so they generally need a higher set temperature to extrude the same material cleanly. If you swapped to hardened steel for abrasive filament and started under-extruding, bump the temperature before blaming anything else.

Flow rate / extrusion multiplier: the core setting

This is the headline number people mean when they search for how to fix under-extrusion settings. Be aware the naming differs across slicers: PrusaSlicer and Simplify3D call it Extrusion Multiplier; Cura calls it Flow (and confusingly uses “flow” for its volumetric preview too — a separate concept).

At 100% the printer extrudes the calculated amount. Calibrating it corrects for small filament-diameter variations so you don’t under- or over-extrude. Usual working values sit between 90 and 110, though you’re not forbidden from going outside that. Crucially, this is a per-filament setting: tune it at minimum per brand and material type. It can even vary by colour or by spool, depending on how consistent your supplier is.

For a quick fix, increase flow by 5% at a time until the gaps close.

The proper flow calibration method

For accuracy, print a thin-walled, single-perimeter hollow cube:

Set flow to 100% and disable retraction.
Measure all four walls with calipers and average them.
Apply the formula: New Flow = (Target Wall Thickness ÷ Measured Wall Thickness) × Current Flow.
Repeat until you’re within ±0.02 mm of the target.

That said — your eyes beat the maths. After the calculation, nudge flow up or down based on what the surface actually looks like. The formula gets you close; the print tells you the truth.

Other settings worth checking

If temperature, E-steps and flow are dialled in and you still see under-extrusion, look at print speed (too fast outruns the hotend’s melt rate — back it off in 10 mm/s steps), partial clogs, and a slipping or under-tensioned extruder gear. Heat creep on long retracts can also starve the nozzle. For neighbouring symptoms that often travel with under-extrusion, see our fixes for first layer adhesion and PETG stringing. Running your file through the gcode pre-flight checklist before you print is a cheap way to catch flow-related issues early.

FAQ

Should I calibrate E-steps or flow rate first?

E-steps first, then temperature, then flow. E-steps corrects the extruder hardware; flow corrects per-filament variance. If you calibrate flow on top of wrong E-steps, you’re compensating for a hardware error with a slicer band-aid that will mislead you on every other filament.

What flow rate should I use to fix under-extrusion?

Most filaments land between 90 and 110% flow. If you’re under-extruding, raise it in 5% steps until the gaps close, then verify with a thin-wall calibration cube and your calipers. Tune it per filament brand and type.

Can low temperature cause under-extrusion?

Yes — it’s one of the most common causes. If the hotend can’t melt filament fast enough, it can’t push the required volume. Raise the nozzle temperature in 5–10 °C steps, and remember hardened steel nozzles usually need to run hotter than brass.

Why does my printer under-extrude suddenly when it was fine before?

That’s almost always mechanical, not a calibration drift — a partial clog, heat creep, or a slipping extruder. Fix the hardware first. Re-calibrating settings to hide it just delays the next failure.