3D print volumetric flow.

Worked example

Line width 0.45 mm and layer height 0.2 mm. The cross-section is a rectangle (0.45 - 0.2) x 0.2 = 0.05 mm2 plus two half circles of diameter 0.2 mm (pi x 0.2 x 0.2 / 4 = 0.0314 mm2), a total of 0.0814 mm2. At 60 mm/s the flow is 0.0814 x 60 = 4.88 mm3/s. With a 15 mm3/s hotend limit the top speed is 15 / 0.0814 = 184 mm/s. Filament feed speed is 4.88 / (pi x 1.75 x 1.75 / 4 = 2.405 mm2) = 2.03 mm/s.

How it works

The plastic laid down per second is the area of the extruded line, seen in cross-section, times how fast the head moves. The calculator models the line as a rectangle with semicircular ends: area = (width - height) x height + pi x height squared / 4. The filament the extruder must feed per second is the same volume divided by the filament's own cross-section.

Slicers use a maximum volumetric speed to slow print moves that would exceed what the hotend can melt: the limited speed is the maximum volumetric speed divided by the cross-section. Signs the limit is too high include extruder clicking, under-extrusion at high speed and poor layer adhesion. Start conservative and raise it gradually.

Sources (opened 2026-10-08). Max volumetric speed | Prusa Knowledge Base for the definition of max volumetric speed as the maximum amount of plastic in mm3/s a hotend can reliably melt, for max speed = MVS / cross-section area, for the stadium-shaped cross-section PrusaSlicer uses, and for the signs of a limit set too high. The filament feed speed is plain geometry. No hotend limit values are published here.

FAQ

What is volumetric flow in 3D printing?

It is the volume of plastic extruded per second, in mm3/s. It equals the extrusion cross-section times the print speed.

What is max volumetric speed?

It is the maximum amount of plastic in mm3/s your hotend can reliably melt, and slicers use it to limit speed on thick or wide extrusions.

How fast can I print with my hotend?

Divide the hotend's max volumetric speed by the cross-section of your line. Taller layers and wider lines allow lower top speeds.

What is my hotend's limit?

It depends on the hotend, nozzle, temperature and filament, so test it or use the maker's data. Start conservative and increase gradually.

Why is the area not just width x height?

The edges of an extruded line are rounded, so the stadium shape (a rectangle with rounded ends) is a better model. It gives a slightly smaller area than width times height.