Pressure advance is one of the most effective calibrations you can run for print quality. It cleans up blobs at corners, fixes the slight over-extrusion at the start of lines, and allows you to print faster without losing quality. If you have noticed that corners on your prints look slightly blobby or rounded, or that line starts look fatter than they should, pressure advance is the fix.
Pressure advance is the Klipper firmware term. Marlin calls the same feature Linear Advance (LA). They work identically - this guide covers both.
When your printer pushes filament into a hot nozzle, the filament is slightly compressible. As the extruder motor pushes, pressure builds up in the hotend before plastic actually comes out. When the extruder slows or stops (at a corner, for example), that built-up pressure continues to push plastic out after the motor has stopped.
The result: blobs and zits at corners, rounded sharp edges, and slightly inconsistent line widths.
Pressure advance compensates for this by pushing filament slightly ahead of where it is needed (to pre-load pressure) and pulling back slightly when decelerating (to release pressure before it oozes out).
Pressure advance is most impactful if you are seeing:
If your prints already look clean, your firmware may have a reasonable default set, or the issue may lie elsewhere.
Klipper's built-in pressure advance tuning print is the fastest method.
Step 1: Add this to your printer.cfg if it is not already there:
[extruder]
pressure_advance: 0.0Step 2: Run the tuning tower. In your Klipper console (Mainsail or Fluidd), run:
SET_VELOCITY_LIMIT SQUARE_CORNER_VELOCITY=1 ACCEL=500
TUNING_TOWER COMMAND=SET_PRESSURE_ADVANCE PARAMETER=ADVANCE START=0 FACTOR=.005Then start a print of a simple hollow square or box shape.
Step 3: Examine the result. The pressure advance value increases as you go up the print. Find the height where corners look cleanest and lines look most consistent, then calculate the value:
Pressure advance = height of best layer x 0.005
Step 4: Set the value in printer.cfg:
[extruder]
pressure_advance: 0.04 # replace with your measured valueTypical values: 0.02-0.08 for direct drive, 0.4-0.8 for Bowden setups.
Marlin's Linear Advance uses K-factor instead of PA value, but the concept is the same.
Step 1: Check that Linear Advance is enabled in your firmware. Many Marlin builds ship with it disabled. If M900 commands in the terminal give an error, LA is not compiled in and you need a custom firmware build.
Step 2: Use the Marlin LA calibration pattern generator at marlinfw.org/tools/lin_advance/. Configure your printer dimensions, generate the G-code, and print it.
Step 3: The print produces a series of lines at different K values. Find the K value where lines are most consistent in width. Set it with:
M900 K0.15 # replace with your measured value
M500 # save to EEPROMTypical K values: 0.05-0.25 for direct drive, 1.0-2.0 for Bowden.
Bambu Lab printers run their own closed firmware that includes pressure advance tuned by the manufacturer. You cannot manually set the PA value in the same way. If you are seeing corner blobs on a Bambu printer, the issue is more likely a flow rate calibration problem - run the built-in flow calibration from the printer menu.
Once pressure advance is set, you may find you can:
Re-run this calibration if you change your extruder hardware, switch between direct drive and Bowden, or install a new hotend - the physical characteristics of the filament path have changed.