Linear Advance vs Pressure Advance: The Ultimate Guide

In the quest for precise and clean 3D prints, extrusion control plays a pivotal role. Despite perfect slicer settings and calibration, many prints still suffer from blobbing, stringing, inconsistent corners, or uneven lines. That’s where Linear Advance (for Marlin firmware) and Pressure Advance (for Klipper and some other firmware) come into play.

These two features are often compared, misunderstood, and sometimes confused as being the same. While they serve the same purpose—improving extrusion accuracy during acceleration and deceleration—they work in slightly different ways depending on the firmware and setup.

This guide breaks down both concepts in detail, compares how they work, and helps you decide which one is right for your 3D printer setup.

Why Do You Need Extrusion Compensation?

In FDM printing, filament is pushed through a nozzle by gears (typically part of a Bowden or direct drive extruder). During motion:

• When accelerating, the pressure inside the nozzle lags, causing under-extrusion.
• When decelerating or stopping, the pressure overshoots, leading to over-extrusion.

This pressure lag results in:

• Blobs at corners
• Gaps on sharp turns
• Uneven walls
• Rounded corners
• Unwanted stringing

To counter this, firmware-level compensation techniques like Linear Advance and Pressure Advance are used to predict and regulate pressure changes, keeping extrusion consistent and sharp.

What is Linear Advance?

Linear Advance is a feature in the Marlin firmware that modifies the extruder’s behavior based on print speed. Instead of pushing filament at a constant rate, Linear Advance increases or decreases the extrusion rate proportionally as the printer accelerates or decelerates.

How It Works:

• Calculates extrusion pressure required for the current motion.
• Adjusts extrusion speed ahead of time, so pressure builds or drops in sync with the movement.
• Uses a constant called the K-factor to determine how aggressively compensation is applied.

Key Benefits:

• Cleaner corners and start/stop points
• Reduced stringing and oozing
• More consistent walls and infill
• Faster printing at high accelerations without quality loss

Firmware Compatibility:

• Marlin-based printers
• Requires enabling in firmware and calibrating K-factor

What is Pressure Advance?

Pressure Advance is a similar concept implemented in Klipper firmware and some others (like Smoothieware). Rather than relying solely on a speed-based algorithm, Pressure Advance compensates more precisely using the printer’s kinematics and pressure model.

How It Works:

• Predicts pressure buildup inside the nozzle based on movement planning and filament compressibility.
• Adjusts the extruder position by moving filament ahead of time during acceleration and retracting slightly during deceleration.
• Uses a Pressure Advance Factor to control how much adjustment is applied.

Key Benefits:

• Extremely clean corners and junctions
• Superior accuracy on complex shapes and sharp transitions
• Ideal for high-speed printing
• Works well with both Bowden and direct drive systems

Firmware Compatibility:

• Klipper firmware
• Also supported in Smoothieware and some RepRap variants

Linear Advance vs Pressure Advance: Core Differences

While both features solve the same problem, their implementation and tuning differ in several ways.

How to Calibrate Linear Advance

Requirements:

• A printer running Marlin firmware with Linear Advance enabled
• Slicer capable of inserting G-code
• A test model or script

Step-by-Step Calibration:

1. Enable Linear Advance in Marlin
   Confirm it’s enabled in your firmware build (#define LIN_ADVANCE in Configuration_adv.h).
2. Use a Calibration G-code Script
   Marlin provides a test G-code that prints multiple lines, each with a different K-factor value.
3. Observe Line Quality
   Look for the sharpest corners without under- or over-extrusion. The K-value that results in the cleanest transitions is your optimal setting.
4. Set the K-Factor
   Add M900 K{your_value} to your slicer’s start G-code or EEPROM.
5. Retest if Needed
   Some filaments require slightly different K-values due to flexibility or friction.

Example Command:

gcodeCopyEditM900 K0.16

How to Calibrate Pressure Advance

Requirements:

• A printer running Klipper firmware
• Access to the Klipper console (via OctoPrint, Fluidd, Mainsail)
• A pressure advance test macro or G-code

Step-by-Step Calibration:

1. Run a Test Print
   Klipper includes macros that create a test pattern with different pressure advance values.
2. Examine Lines or Corners
   Look for the setting that produces clean, sharp corners without gaps or blobs.
3. Apply the Value
   Use SET_PRESSURE_ADVANCE ADVANCE={value} in the console or in the config file under your extruder section.
4. Tune Per Filament
   Different materials, especially TPU or flexible filament, need different compensation levels.
5. Recheck With Real Models
   Use actual prints with lots of travel and sharp turns to validate the setting.

Example Command:

gcodeCopyEditSET_PRESSURE_ADVANCE ADVANCE=0.06

Direct Drive vs Bowden: What’s the Impact?

The type of extruder setup has a major impact on how well these features work and what values are typical.

Bowden setups suffer more from pressure lag due to the long filament path and tube flex, making Linear/Pressure Advance even more beneficial.

Use Cases: When Should You Use It?

Ideal Scenarios:

• High-speed printing
• Geometries with sharp angles or rapid travel moves
• Flexible filaments that compress under pressure
• Tall prints with long, straight walls
• Infill inconsistencies or seams on start/stop points

When It’s Less Important:

• Slow printing speeds (<40 mm/s)
• Low-detail models with minimal motion changes
• Basic printers with unmodified firmware
• Slicers already tuned for low acceleration

Still, in most real-world use cases, some level of pressure compensation improves quality without downside.

Complementary Features and Tuning

To get the most out of Linear or Pressure Advance, pair it with these:

• Input Shaping (Klipper): Minimizes vibrations and ringing
• Junction Deviation or Classic Jerk: For smoothing motion transitions
• Retraction Tuning: Needed to avoid overlap with pressure adjustment
• Acceleration Calibration: Affects how aggressively the nozzle moves

Together, these features make your printer behave more predictably and consistently across complex models.

FAQs: Linear Advance vs Pressure Advance

Do I need both Linear and Pressure Advance?
No. They are firmware-specific. Use Linear Advance with Marlin, and Pressure Advance with Klipper.

Is one better than the other?
Pressure Advance (in Klipper) is generally more precise due to its predictive model, but both produce excellent results when tuned correctly.

Can I use them with flexible filament?
Yes, and it’s recommended. TPU and other flexibles benefit significantly from extrusion compensation.

Do I need to re-tune for each filament?
Ideally, yes. Different materials compress and extrude differently.

What happens if I over-tune it?
You may see under-extrusion at corners, gaps in infill, or weakened layer bonds. Adjust values gradually.

Conclusion

Linear Advance and Pressure Advance are essential tools in fine-tuning the extrusion performance of your 3D printer. While they serve the same function—compensating for pressure lag—they are specific to different firmware ecosystems and use slightly different approaches to achieve clean, consistent, and precise prints.

• Use Linear Advance if you’re on Marlin firmware, especially with Bowden setups or sharp-featured models.
• Use Pressure Advance on Klipper firmware to push speed, precision, and efficiency to new levels.

Tuning either feature correctly can eliminate some of the most frustrating issues in FDM printing, including blobby corners, inconsistent walls, and stringing. It’s one of the smartest upgrades you can make—without changing a single hardware component.