Max Print Speed from Hotend Flow Rate

Every hotend has a maximum rate at which it can melt plastic, measured in cubic millimeters per second (mm³/s). Push faster than that limit and filament enters the nozzle faster than it melts.
What follows is under-extrusion, weak layers and grinding at the extruder.

Volumetric flow and print speed. The relationship is:

V_flow (mm³/s) = layer_height x line_width x print_speed

Rearranging: max_speed = V_max / (layer_height x line_width)

Line width is typically 100-120% of nozzle diameter. This calculator uses 110%, so a 0.4 mm nozzle gives a 0.44 mm line: max_speed = V_max / (0.2 x 0.44)

At V_max = 10 mm³/s that gives 114 mm/s. At V_max = 25 mm³/s it gives 284 mm/s.

Hotend limits (approximate). Standard all-metal or PTFE-lined V6-style: 10-15 mm³/s. Volcano-style longer melt zone: 20-30 mm³/s. High-flow hotends (Dragon HF, Rapido, Bambu): 25-40 mm³/s. Bambu X1 series hotend: up to 35 mm³/s in practice.

Material factor. Not all filaments melt at the same rate. PLA is the easy one, flowing freely above 200°C. PETG needs slightly more heat. ABS, ASA, and Nylon need higher temperatures and benefit from shorter melt zones at high speeds. The material factor scales the effective V_max down for harder-to-melt materials.

Practical limit. The calculated speed is a thermal ceiling only. Motion system (resonance, belt tension), part cooling, and layer adhesion all impose lower real-world limits. Many printers run at 50-70% of their thermal ceiling for quality reasons.