What Is Pressure Advance and How Do You Calibrate It?

Pressure advance is a firmware setting that pushes extra filament into the nozzle as the print head speeds up and pulls it back as it slows down, so extrusion keeps up with movement. It reduces bulging corners and ooze, and you tune one number per extruder, nozzle and filament.

This guide explains what the setting does, what it is called on each firmware, and how the main slicer and firmware calibration methods work. Everything comes from Klipper, Marlin, Prusa and OrcaSlicer documentation, not from our own test prints.

What is pressure advance?

Molten plastic in a nozzle behaves like a slightly squeezed spring. When the extruder pushes, pressure builds before plastic flows out evenly, and when the extruder stops, plastic keeps oozing. Klipper's documentation says pressure advance reduces ooze during non-extrude moves and reduces blobbing at corners. It does this by pushing in extra filament during acceleration and retracting it during deceleration.

Marlin describes its version, Linear Advance, as a way to manage the pressure inside the nozzle as print speed changes. It lists less bleeding at corners and rougher solid infill, and it allows higher print speeds without losing quality. Prusa says its Pressure Advance aims to improve printed part quality by offsetting nozzle pressure changes.

Klipper also notes that pressure advance does not change print time or the total amount of filament extruded. It only reshapes when the filament moves.

What is pressure advance called on each firmware?

The idea is the same everywhere, but the name, command and number scale differ. Do not copy a value from one system to another.

Prusa says Pressure Advance replaces Linear Advance on the MK4/S, MK3.9/S, XL and MINI/+ from firmware 5.0.0. Older M900 K commands still work there and are converted 1:1 to a pressure advance value. Printers that run Klipper expose the setting directly, and many ship with a sensible default.

Why do corners bulge without it?

At a corner the toolhead slows, turns and speeds up again. Without compensation the extruder keeps feeding at a steady rate while the head slows, so pressure builds and a bulge forms. Then the head accelerates away and the nozzle is briefly starved. Klipper uses corner blobbing as its tuning signal for exactly this reason.

If you see bulges at corners, thin spots after them or oozing between features, pressure advance is one possible cause. Other causes include too much flow and retraction settings, so compare with fixing blobs and zits, fixing over-extrusion and retraction settings explained.

Does pressure advance replace retraction?

No. Pressure advance handles pressure changes while the nozzle is printing, and retraction pulls filament back before a travel move. Klipper says the setting reduces ooze during non-extrude moves, so you may be able to use a smaller retraction afterward, but the two features work together. If stringing remains after tuning, read how to fix stringing.

How do you calibrate pressure advance?

You calibrate pressure advance by printing a test that varies the value, finding the section with the cleanest corners or most even lines, and entering that value in your firmware or filament profile. The right number depends on the extruder, nozzle, filament brand and even pigment, so each filament may need its own value.

Klipper's documentation says to tune rotation_distance and nozzle temperature first. Marlin's says to calibrate steps per millimeter first and keep gear and fitting backlash low. Both sources say to recalibrate when filament, temperature or hardware changes. The general process is in our printer calibration guide.

Klipper tuning tower

Klipper's steps are:

1. Slice the hollow square tower from the Klipper docs at about 100 mm/s, with zero infill and a layer height near 75% of the nozzle diameter. Turn off dynamic acceleration control and scarf joint seams.
2. Run SET_VELOCITY_LIMIT SQUARE_CORNER_VELOCITY=1 ACCEL=500.
3. Start the tower with TUNING_TOWER COMMAND=SET_PRESSURE_ADVANCE PARAMETER=ADVANCE START=0 FACTOR=.005 for direct drive, or FACTOR=.020 for Bowden.
4. Measure the height of the best corners with calipers. If unsure, take the lower height.
5. Calculate pressure_advance = start + measured height x factor. The docs give 0 + 12.90 x 0.020 = 0.258 as an example.
6. Save the value in the [extruder] section and issue RESTART.

Klipper adds that if there is no clear improvement up to 1.000, pressure advance is unlikely to help and should be disabled. Values above about 0.200 may cause extruder skipping when returning to normal acceleration, so lower the acceleration or disable it in that case.

OrcaSlicer calibration tests

OrcaSlicer's wiki lists three methods, each with direct drive and Bowden versions. See our OrcaSlicer beginner guide for the rest of the calibration menu.

• Line method: quick and simple, but accuracy depends heavily on first layer quality, so bed mesh leveling is recommended. Pick the most even line and enter that value. The wiki's example found 0.016.
• Pattern method: based on Andrew Ellis' generator, which derives from Marlin's pattern, and can run several tests in a batch.
• Tower method: does not depend on the first layer but takes longer. The formula is PA = start + (step x measured height). With a start of 0, a step of 0.002 and a height of 8 mm, the result is 0.016.

OrcaSlicer also notes that Marlin printers need Linear Advance enabled with M900, that Bambu Lab printers should leave the flow calibration option unchecked, and that the result should be saved to the material profile. For high-speed printers it points to Adaptive Pressure Advance as possibly more accurate.

Marlin K factor

Marlin's page says the best K is the one where the transition between slow and fast sections looks smooth, with no starved or over-extruded area. Add M900 Kxx to the slicer start G-code to set K per material, and set LIN_ADVANCE_K to 0 in firmware so only your value applies. Turn off slicer options that interfere, such as coasting and wipe.

Is pressure advance different for direct drive and Bowden?

Yes. Both Klipper and Marlin say Bowden extruders need higher values than direct drive, because there is more compressible filament between gear and nozzle. Klipper's tower factor is four times larger for Bowden (0.020 against 0.005). Marlin adds that Bowden setups are more likely to hit its acceleration limits and are less precise. See direct drive versus Bowden for the hardware difference.

Common questions about pressure advance

Input shaping is a separate feature that targets ringing, not corner bulges. If you see ripples after sharp corners, read fixing ghosting and ringing. Use our print cost calculator if you want to see what failed test prints cost in filament.