3D Print Nozzle Flow Calculator

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.

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.