3D Printing Flow Rate: What it is and Calibration Guide

Mario De Lio

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White filament oozing from the nozzle of an FDM 3D printer

Flow rate, also known as the extrusion multiplier, determines the amount of filament extruded during printing. A well-calibrated flow rate ensures proper layer bonding, smooth surface finishes, and dimensional accuracy.

Different filaments and materials have varying flow characteristics.

Calibrating the flow rate can help prevent common printing issues such as over-extrusion, under-extrusion, and stringing.

Here’s everything you need to know about the 3D printing flow rate.

3D Printing Flow Rate Basics

White filament oozing from the nozzle of an FDM 3D printer

3D printing flow rate, also known as the extrusion multiplier, determines the amount of filament extruded by the hot end. Flow rate is generally presented as a numerical percentage, with the default value set at 100% or 1.0, depending on the slicing software.

Adjusting the flow rate can directly impact the quality and accuracy of your 3D prints.

Printing with the incorrect flow rate can lead to common printing issues like:

  • Over-extrusion
  • Under-extrusion
  • Layer delamination
  • Stringing, zits, and blobs
  • Poor first-layer adhesion

The flow rate helps control the balance between print speed and quality.

It is beneficial for fixing issues regarding over and under-extrusion.

As a quick guide, if you’re getting over-extrusion in your prints, lower the flow rate by 5%. With under-extrusion, increase the flow rate by 5%.

This method requires some experimentation to achieve the desired results without compromising the integrity of the print. Below we’ll cover how to calibrate the flow rate best.

How To Calibrate Flow Rate

Required Materials

A caliper, marker, snips, and calculator required for calibrating the E-steps
  • Measuring tool (preferably a digital vernier caliper or a ruler that can measure in millimeters) (Amazon link)
  • Calculator
  • Felt tipped pen

Now That you understand the importance of calibrating your flow rate follow the steps below to optimize your 3D prints.

Step 1: Measure the Filament Diameter

Before beginning the flow rate calibration, you must check the filament diameter. You can find the diameter listed on the side of the filament spool or use a caliper for an accurate measurement.

Most commonly, 3D printing filaments have a thickness of 1.75 mm, with slight variations caused by the manufacturing process.

Step 2: Print The Hollow Test Cube

The hollow test cube from Thingiverse used to calibrate 3D printer flow rate
(Source: petrzmax via Thingiverse)

Download the hollow test cube from Thingiverse and import the file into your slicing software.

Import the file into your slicer software and print it with the flow rate set to 100%.

Step 3: Measure the Wall Thickness

Checking the flow rate using a test print and digital caliper
(Source: petrzmax via Thingiverse)

After completing the print, measure the thickness of each wall using a digital caliper and take the average of the four values.

The average value should be 0.8mm if our flow rate is correct.

If the measured thickness differs from 0.8mm, we must adjust the flow rate.

To calculate our new flow rate, we’ll use the following formula:

New Flow Rate = (Expected Wall Thickness / Measured Wall Thickness) * Current Flow Rate

For example, if the measured thickness is 1.0 mm when it should be 0.8 mm, decrease the flow rate by multiplying it by the ratio of the expected to the measured thickness.

New Flow Rate = (0.8 / 1.0) * 100 = 80

Enter the net flow rate into the slicer software.

Step 4: Re-Print the Test Cube

Once you adjust the flow rate, printing the test cube again and measuring the wall thickness is a good idea. Repeat steps two and three until the measured thickness is close to the expected value.

Any time we adjust our 3D printer or slicer settings, it’s best to run a test to ensure our printer is working correctly.

We must repeat the process as many times as necessary to get the correct flow rate settings.

*Note: Print speed significantly impacts setting the correct flow rate. The faster the print head moves, the less time filament accumulates on the previous layer. If you change the print speed, you may need to adjust the flow rate.

Best Flow Rate By Material

In this section, we’ll look at the optimal flow rates for popular 3D printing filaments.

The numbers below should serve as a general starting point in your calibration process. As always, it’s best to test and calibrate as different 3D printers and filament brands have different optimal flow rates.

What is The Best Flow Rate for PLA?

Generally, the best flow rate for PLA is 100%.

If your prints have over or under-extrusion, you’ll want to calibrate your e-steps and 3D printing temperature.

You should usually adjust the flow rate within the 90-110% range. But as always, running a test print when you adjust your slicer settings is a good idea.

What is The Best Flow Rate for PETG?

We’ve found that PETG performs best with a flow rate of 100%.

PETG filament requires more fine-tuning than PLA, and it’s generally more challenging to work with. We don’t recommend adjusting the flow rate when printing with PETG. Instead, it’s usually best to fix under and over-extrusion by calibrating the e-steps and printing temperature.

But, if you make adjustments, you can get good results with a 95-105% flow rate.

What is The Best Flow Rate for ABS?

ABS material also performs best with a 100% flow rate. Printing with a 90-110% flow rate allows for a steady flow of molten filament, compensating for the material’s tendency to warp.

Tips for Adjusting Flow Rate

The hollow test cube from Thingiverse used to calibrate 3D printing flow rate
(Source: petrzmax via Thingiverse)

Flow Rate and Print Speed

Print speed is a critical factor to consider when calibrating flow rate.

Faster print speeds require higher flow rates to maintain proper extrusion and prevent under-extrusion. The opposite is true for slower printing speeds.

That’s because the faster the hot end moves, the less time it spends over each point in the print. With less time to extrude filament, you may run into under-extrusion issues.

Flow Rate and Nozzle Diameter

The nozzle diameter is crucial in determining the ideal flow rate for your 3D printer. You should adjust the flow rate depending on the nozzle diameter to ensure a consistent extrusion width. For example, with a 0.4mm nozzle and a flow rate of 100% (1), the thickness of a single wall should be 0.4mm.

Some experts suggest setting your extruder wall width to 120% of your nozzle opening and increasing the overlap between walls and skin to achieve better flow rate values. So, for a 0.4mm nozzle, use a 0.48mm line width.

Flow Rate and Layer Height

Layer height is another critical factor to consider when adjusting the flow rate. The layer height determines the thickness of each layer in your print, and it should be compatible with your nozzle diameter and flow rate settings. A higher layer height sometimes necessitates a higher flow rate for proper extrusion.

When adjusting the flow rate based on layer height, it’s crucial to stay within the maximum flow capacity of your nozzle. For example, a larger layer height with higher flow rates may not work well with smaller nozzles, leading to under or over-extrusion. Experiment with different flow rates and layer heights to find the optimal balance for your print.

By carefully considering print speed, nozzle diameter, and layer height, you can optimize your flow rate settings for the best 3D print quality. Just make sure not to make exaggerated or false claims and utilize a confident, knowledgeable, and neutral tone of voice.

Identifying Flow Rate Issues

3D printing flow rate plays a crucial role in the quality of prints. This section will discuss common flow rate issues that can impact print quality, how to identify them, and how they relate to the extrusion multiplier.


Over-extrusion occurs when the 3D printer extrudes more plastic than necessary, resulting in thicker or blobby print layers. Over-extrusion can lead to issues like:

When over-extrusion is an issue, try adjusting the extrusion multiplier or flow rate to a lower value, usually by reducing it by 5% to 10% in your slicer settings.


Under-extrusion is when the printer extrudes less plastic than needed, causing thin print layers and possible gaps between layers. Signs of under-extrusion include:

  • Thin or missing layers
  • Rough and uneven print surface
  • Incomplete infill patterns

To fix under-extrusion, increase the extrusion multiplier (the flow rate) by 5% to 10% in your slicer settings.

Layer Delamination

Layer delamination happens when the print layers don’t adhere properly to each other, resulting in weak bonds between layers. Factors contributing to layer delamination include:

  • Incorrect flow rate settings
  • Inconsistent extrusion temperature
  • Incorrect cooling settings

Adjusting the extrusion multiplier, temperature, and cooling settings can help alleviate layer delamination issues.

Poor Bridging

Bridging is the process of printing a horizontal span without support material underneath. Poor bridging can occur due to inadequate flow rate settings, leading to:

  • Sagging or drooping bridges
  • Incomplete bridge structures
  • Unwanted strings or filament strands

To improve bridging performance, adjust the extrusion multiplier and experiment with bridging-specific slicer settings, such as reducing print speed and cooling settings.

Poor Bed Adhesion

Poor bed adhesion can result from inaccurate flow rate settings, causing prints to not stick well to the printing surface. Common symptoms include:

  • Prints detaching from the bed during printing
  • Warping or curling edges
  • Inconsistent first-layer thickness

To address bed adhesion issues, adjust the extrusion multiplier and consider changes to bed temperature, first layer height, and print speed. Proper bed leveling is also crucial for good adhesion.

Testing and Troubleshooting

When working with 3D printing, flow rate calibration is critical to ensure accurate and consistent print quality. One easy and effective method to test the flow rate is printing a test cube and measuring its wall thickness with calipers.

First, import a test cube file into your slicing software and modify your slicer settings accordingly. The wall thickness of the print should be equal to the nozzle size, so if you’re using a 0.4mm nozzle, your single wall thickness should be 0.4mm as well. If the printed wall thickness doesn’t match the expected value, you must update the flow rate settings in Cura or your preferred slicer software.

While measuring the printed test cube’s wall thickness, it’s essential to use a precise measuring tool like a caliper. Carefully measure the thickness at multiple points to get an average value. Once obtained, input the data into the following formula:

New Flow Rate = (Expected Wall Thickness / Measured Wall Thickness) * Current Flow Rate

For example, assume your current flow rate is 100%, and you measure a wall thickness of 0.45mm. The new flow rate would be calculated as follows:

New Flow Rate = (0.4 / 0.45) * 100 = 88.89%

Once the new flow rate value is calculated, update the flow rate setting in your slicing software and perform another test print. This process may need to be repeated a few times until the proper wall thickness is achieved.

While troubleshooting, keep in mind the following tips:

  • Ensure the filament diameter is correctly set in the slicer software.
  • Check the extrusion multiplier or flow rate for accuracy.
  • Verify that your nozzle size is accurate and that it’s not worn out or clogged.
  • Print at a consistent speed to avoid thickening or thinning of the walls.

With careful testing and troubleshooting, you can achieve an accurate flow rate for your 3D printer and improve the overall print quality.

Article by

Mario De Lio

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