How to use the 3d print flow rate calculator
- Enter the line width, layer height and print speed from your slicer.
- Enter your hotend's flow limit in cubic millimeters per second, if you know it.
- In More options, add the filament diameter, the plastic volume of the print and the filament density.
- Read the flow, the filament feed speed, the share of the limit used and the fastest speed within the limit.
Formula
Cross-section = line width x layer height
Volumetric flow = cross-section x print speed
Filament feed speed = flow / (pi x filament radius squared)
Fastest speed within the limit = flow limit / cross-section
Flow is in cubic millimeters per second when widths and heights are in millimeters and speed in millimeters per second.
Three settings
A 0.4 mm line, 0.2 mm layer and 100 mm/s speed makes 0.08 mm2 of line and 8 mm3/s of flow. With 1.75 mm filament, it feeds at 3.326 mm/s. Against a limit of 15 mm3/s that is 53 percent, so the speed could rise to 187.5 mm/s. A print of 30 cm3 takes 1 h 02 min at that flow, uses 12.47 m of filament and weighs 37.2 g at 1.24 g/cm3.
Dropping to a 0.15 mm layer with a 0.42 mm line at 250 mm/s gives 15.75 mm3/s, which is 105 percent of a 15 mm3/s limit, so the hotend would likely under-extrude. A 0.9 mm line with a 0.4 mm layer at 60 mm/s is 21.6 mm3/s, 90 percent of a 24 mm3/s limit.
Why flow rate limits speed
A hotend can melt only so much plastic each second. Speed alone does not tell you how much it needs, because a thick layer or wide line at a moderate speed asks for as much as a thin layer at a high one. Volumetric flow puts them on the same scale, so you can compare settings and see which one is the real bottleneck.
Filament length and weight conversions are in the filament length to weight calculator. For other flow rates see the flow rate calculator, for printed image sizes the image DPI print size calculator, and for solid parts the metal weight calculator.
Finding your own limit
Published limits are rough because they depend on the nozzle, the temperature, the filament and its color. A common way to find yours is to extrude into the air at increasing speed until the extruder starts to click or the line thins, then back off. The number you enter is only as good as that measurement, and the 15 mm3/s in the examples is only an example.
Assumptions and limits
- The extrusion is modeled as a rectangle of line width times layer height, which slightly overstates the cross-section of real rounded lines.
- Acceleration and corners slow the nozzle below the set speed, so real flow is often lower than shown.
- Filament density defaults to 1.24 g/cm3 as an example for PLA. Use the value on your filament.
- No temperature or material effects on the hotend limit are modeled.
Frequently asked questions
What is volumetric flow rate in 3D printing?
It is the volume of plastic extruded per second, equal to the line width times the layer height times the print speed. It shows how hard the hotend has to work.
How do I find the maximum print speed for my hotend?
Divide the hotend's flow limit by the line width times the layer height. With a 15 mm3/s limit and a 0.4 by 0.2 mm line that is 187.5 mm/s.
What happens if the flow is too high?
The hotend cannot melt plastic fast enough, so the extruder under-extrudes or skips. You will see thin lines, gaps and weak layers. Slow down or use a thinner layer.
How is filament speed related to flow?
Filament enters the hotend as a round cylinder. Its feed speed is the flow divided by the cross-section of the filament, so thicker filament feeds more slowly for the same flow.