Why mm³/s is the real speed limit
A hotend can only melt so much plastic per second. Print speed in mm/s means nothing on its own: 150 mm/s at 0.1 mm layers is easy, but at 0.3 mm layers it is three times the plastic.
Flow (mm³/s) = layer height × line width × speed
Max speed = hotend max flow ÷ (layer height × line width)
Example: 0.2 mm × 0.45 mm × 150 mm/s = 13.5 mm³/s, just within a standard hotend's 15 mm³/s. At 0.28 mm layers the same speed needs 18.9 mm³/s.
Set the max volumetric speed in your slicer's filament profile and it will slow down automatically when needed.
Frequently asked questions
What is a good max volumetric flow for PLA?
About 12–15 mm³/s on standard hotends, 20–30 on Bambu Lab and 25–35 on Volcano/CHT nozzles.
How do I find my hotend's max flow?
Print a flow test tower that increases speed until the extrusion drops, or use the max volumetric speed test in Orca Slicer.