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3D Print Nozzle Flow Calculator

Enter your layer height, line width and print speed.

How it is calculated

Plastic leaves the nozzle as a ribbon whose cross-section is layer height times line width, moving at the print speed. So flow = layer height × line width × print speed, with the two lengths in mm and the speed in mm/s, giving mm³/s. That flow is compared with the hotend's maximum melt flow (also mm³/s); if the max-flow box is left empty, 15 is used. The tool answers "OK" when the flow is at or below the limit and "Exceeds max" when it is above. A result that lands exactly on the limit, such as 0.2 × 0.4 × 150 = 12 against a limit of 12, is treated as OK. It also turns the formula around: max speed = max flow / (layer height × line width). All values must be greater than zero, otherwise no result is shown. The model is a single extrusion line and ignores acceleration, retraction and filament type.

Worked example

Layer height 0.2 mm, line width 0.45 mm, speed 200 mm/s, hotend limit 12 mm³/s. Cross-section: 0.2 × 0.45 = 0.09 mm². Flow: 0.09 × 200 = 18.00 mm³/s. That is above 12, so the check shows "Exceeds max". The fastest speed within the limit is 12 / 0.09 = 133.33 mm/s, so the print needs to slow from 200 to about 133 mm/s or less.

Try this example →

Common mistakes

  • Entering the nozzle diameter as the line width without checking the slicer; a 0.4 mm nozzle is often sliced with 0.42 or 0.45 mm lines, which raises the flow by 5 to 12 percent.
  • Typing the speed in mm/min, as some firmware and G-code use, instead of mm/s; 12000 mm/min is 200 mm/s.
  • Using the max-flow figure of a different filament or temperature; the limit is not a property of the printer alone, so a PLA number is too high for tougher materials at the same heat.
  • Checking only the headline speed; first layer, infill and outer wall speeds differ, and each one has its own flow.
  • Leaving the max-flow box empty and assuming your hotend's value was used; the tool falls back to 15 mm³/s.

About this calculator

A 3D printer's volumetric flow rate is how fast molten filament passes through the nozzle, calculated as layer height × line width × print speed. Every hotend has a maximum melt flow rate — how fast it can actually heat and push plastic — typically 10-15 mm³/s for a stock brass nozzle on filaments like PLA, and lower for harder materials like PETG or ABS.

This calculator computes your print's required flow rate from your slicer settings and compares it against your hotend's rated max melt flow, warning you if you're asking for more plastic than the hotend can melt in time — a common cause of under-extrusion and skipped layers. 3D printing hobbyists tuning print speeds use it to push speed as high as possible without exceeding what the hardware can actually deliver.

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  • Editorial team

    You can find your own hotend's limit with this tool. Raise the speed in a test print until under-extrusion first appears, then enter that failing speed along with your layer height and line width. The flow shown is roughly your real ceiling, and you can run slightly below it. What nozzle, filament and flow limit have you settled on for your printer?

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