From hotend specs, or measured via flow test
Usually equals nozzle diameter

Max Safe Print Speed
mm/s
Common Hotend Flow Ratings
Hotend Max Flow (mm³/s) Category
Creality stock (MK8 style)10–14Budget
E3D V612–18Standard
E3D Revo Six20–24Standard
Bambu X1C / P1P18–22High speed
Dragon SF / HF18 / 28Standard / High flow
Rapido HF40–50High flow
Volcano (E3D)40–60High flow (long melt zone)
Goliath / CHC Pro55–70Ultra high flow

Ratings vary by temperature, filament type, and nozzle size. Higher temperatures and larger nozzles increase effective max flow. Values above are for PLA at rated print temperature with a 0.4mm nozzle.