Flow Rate Calibration: Dialling In Extrusion Multiplier

Jackson B.

The Foundation of Print Quality

Your slicer calculates exactly how much filament should pass through the nozzle for every millimetre of print movement. It does this using the nozzle diameter, extrusion width, and layer height to determine the theoretical volume of plastic needed to fill each path correctly.

The extrusion multiplier, also known as flow rate, is a percentage based adjustment applied to those calculations. At 100%, the printer attempts to extrude the exact theoretical amount of material. In reality, however, no printer is perfectly accurate. Filament diameter varies slightly between spools, extruder gears wear over time, and hotend designs never behave exactly like the idealised mathematical model used by the slicer. Flow rate calibration exists to compensate for these small but important real world differences.

An incorrect flow rate is often a subtle problem. Prints may still look mostly acceptable, but surfaces can appear slightly uneven, dimensions may be marginally inaccurate, and overall part strength can suffer. Many makers spend hours adjusting temperatures, retraction settings, or cooling while the real issue is only 3–5% over or under extrusion.

Flow rate calibration is one of the quickest and most effective tuning steps you can perform. In around 20 minutes, it can permanently resolve a whole category of print quality issues for a specific filament and printer setup.

The Single Wall Calibration Method

Print a simple 20 × 20 × 20 mm cube using the following settings:

• 1 perimeter or wall
• 0% infill
• 0 top layers
• Enough bottom layers to keep the print stable

The result should be a hollow cube with a single wall shell.

Once printed, measure the wall thickness at several different points using digital callipers with 0.01 mm precision. Avoid measuring near the very bottom or top of the print, as those areas are often less consistent. Mid height measurements usually give the most accurate results.

Next, compare the measured wall thickness to the value your slicer was expecting to produce. In most cases, the expected wall thickness is calculated from the nozzle diameter and the extrusion width. For a standard 0.4 mm nozzle using an extrusion width of around 105–120%, the expected wall thickness is typically around 0.42–0.48 mm.

For example, if your slicer expected a 0.45 mm wall but the measured wall thickness is only 0.40 mm, the printer is under extruding by roughly 11%.

You can calculate the correction like this:

• 100% × (0.45 ÷ 0.40) = 112.5%

In this case, you would increase the flow rate to around 112% and print the test again.

Repeat the process until the measured wall thickness matches the expected value within approximately 0.02 mm. Once achieved, you now have a properly calibrated flow rate for that specific filament and printer setup.

Per-Material and Per-Temperature Variation

Flow rate calibration can vary noticeably between different filament types and even between different brands of the same material. For example, PLA might calibrate perfectly at 100%, while PETG from the same manufacturer may produce better results closer to 97%. Flexible materials such as TPU often require higher flow rates around 105–110% because the filament can compress and slip slightly inside the extruder due to its softer, more elastic nature.

Printing temperature also affects flow rate. Higher nozzle temperatures generally allow plastic to flow more easily, which can slightly increase the effective extrusion rate. Because of this, it is important to complete your temperature calibration first, then calibrate flow rate using the final temperature you actually intend to print at. Once calibrated, record the values and apply them consistently for that specific filament profile. Proper profile management makes it much easier to maintain predictable print quality across different materials and brands. To organise these settings systematically, see our profile management guide.

For the most accurate overall extrusion calibration, it is also recommended to calibrate your e-steps before adjusting flow rate.