Volumetric flow calculator for 3D printers: mm³/s to print speed

The formula

A printed line is a thin strip of plastic. Its cross-section times the speed the nozzle moves gives the plastic per second:

volumetric flow (mm³/s) = layer height (mm) × line width (mm) × print speed (mm/s)
max print speed (mm/s)  = max volumetric speed (mm³/s) ÷ (layer height × line width)
filament feed (mm/s)    = flow ÷ (π × (filament diameter ÷ 2)²)

The first line is the formula Bambu Lab’s wiki gives. When Bambu Studio and OrcaSlicer enforce the cap, they model the line as a rectangle with rounded ends instead (Flow::mm3_per_mm in both slicers’ source):

slicer cross-section = layer height × (line width − layer height × (1 − π/4))
                     ≈ layer height × (line width − 0.215 × layer height)

At 0.2 × 0.45 mm that is 0.0814 mm² instead of 0.09 mm², so the slicer’s own speed cap sits about 11% higher than the plain rectangle gives. Pick “Rounded” in the calculator to match the slicer.

How do you calculate volumetric flow rate in 3D printing?

Multiply layer height by line width by print speed, all in millimeters. The result is cubic millimeters of plastic per second. A 0.2 mm layer with a 0.45 mm line at 200 mm/s flows 0.2 × 0.45 × 200 = 18 mm³/s, the worked example in Bambu Lab’s wiki. At 300 mm/s the same line needs 27 mm³/s.

Worked example: the calculator’s defaults

1. Cross-section: 0.2 × 0.45 = 0.09 mm².
2. Flow at 200 mm/s: 0.09 × 200 = 18 mm³/s.
3. Against Bambu Studio’s generic PLA profile, which uses 12 mm³/s: 18 ÷ 12 = 150% of the limit.
4. The slicer slows that line to 12 ÷ 0.09 = 133 mm/s (147 mm/s with the rounded cross-section).
5. Filament fed into the extruder: 18 ÷ 2.405 = 7.48 mm/s of 1.75 mm filament.

Layer height moves flow as much as speed does. With a 0.45 mm line:

Layer height	100 mm/s	200 mm/s	300 mm/s
0.12 mm	5.4 mm³/s	10.8 mm³/s	16.2 mm³/s
0.20 mm	9 mm³/s	18 mm³/s	27 mm³/s
0.28 mm	12.6 mm³/s	25.2 mm³/s	37.8 mm³/s

Use the line width of the feature you are checking. Slicers set walls, infill and top surfaces separately. The widest and fastest feature reaches the limit first.

How do you convert max volumetric speed to print speed?

Divide the max volumetric speed by layer height times line width. Bambu Studio’s generic PLA (polylactic acid) profile uses 12 mm³/s, so at a 0.2 mm layer and 0.45 mm line that flow allows 12 ÷ 0.09 = 133 mm/s. The slicer slows any line set faster down to that speed.

Max print speed for each preset

All at a 0.2 mm layer and 0.45 mm line. The rounded column is what the slicer itself computes.

Preset	Max volumetric speed	Max speed, rectangle	Max speed, rounded
Bambu Studio, Generic PLA Silk	7.5 mm³/s	83 mm/s	92 mm/s
Bambu Studio, Generic PLA	12 mm³/s	133 mm/s	147 mm/s
Bambu Studio, Generic PETG	12 mm³/s	133 mm/s	147 mm/s
Bambu Studio, Generic ASA	12 mm³/s	133 mm/s	147 mm/s
Bambu Studio, Generic ABS	15 mm³/s	167 mm/s	184 mm/s
Bambu Studio, Generic PC	16 mm³/s	178 mm/s	197 mm/s
Bambu Studio, Generic TPU	3.2 mm³/s	36 mm/s	39 mm/s
Bambu Studio, Bambu PLA Basic (X1C)	21 mm³/s	233 mm/s	258 mm/s
Bambu Studio, Bambu PETG HF (X1C)	21 mm³/s	233 mm/s	258 mm/s
Bambu Lab Standard Flow hotend 0.4 mm, PLA Basic	24 mm³/s	267 mm/s	295 mm/s
Bambu Lab High Flow hotend 0.4 mm, PLA Basic	40 mm³/s	444 mm/s	491 mm/s
E3D Revo 0.4 mm nozzle, PLA	13 mm³/s	144 mm/s	160 mm/s
E3D Revo High Flow 0.4 mm nozzle, PLA	16 mm³/s	178 mm/s	197 mm/s

OrcaSlicer’s calibration guide treats its test result as a best case and suggests setting 10 to 20% lower. The calculator shows that margin as a speed range: 107 to 120 mm/s for the generic PLA example.

Where the preset values come from

The Bambu Studio values come from the profile files in Bambu Lab’s BambuStudio repository, as they load for an X1 Carbon with a 0.4 mm nozzle. Generic PLA inherits 12 mm³/s at 220 °C from fdm_filament_pla.json. Bambu PLA Basic’s X1C profile lists 21 mm³/s for the standard nozzle and 29 for the high-flow extruder variant, both at 220 °C. Bambu PETG HF lists the same 21 and 29.

The Bambu Lab hotend figures come from the store page for the High Flow hotend for the H2, P2S and X2D. It lists 0.4 mm figures for three filaments:

Filament	Standard Flow hotend	High Flow hotend
PLA Basic	24 mm³/s	40 mm³/s
PLA Matte	28 mm³/s	48 mm³/s
PETG HF	24 mm³/s	32 mm³/s

The 0.6 and 0.8 mm High Flow nozzles are listed at 40 mm³/s for all three. The same page says the High Flow hotend fits the A1 and A2 series but does not raise their volumetric speed.

The E3D figures come from E3D’s Revo High Flow post of May 2023, tested with Prusament PLA. E3D says it tests with PLA because PLA is harder to push to high flow than PETG or ASA.

Why the real limit depends on temperature and material

Max volumetric speed is how fast the hotend can melt filament, and that depends on the material. Bambu Lab’s wiki says the limit can only be found by testing. PLA melts quickly and runs thin. PETG (polyethylene terephthalate glycol) and ABS (acrylonitrile butadiene styrene) take longer to melt and run thicker. TPU (thermoplastic polyurethane) buckles when pushed fast and has the lowest limit of all.

Published figures show the spread. E3D measured its Revo High Flow 0.4 mm nozzle at 16 mm³/s with PLA, 26 with ASA (acrylonitrile styrene acrylate) and 27 with PETG. On Bambu Lab’s Standard Flow 0.4 mm hotend, PLA Matte runs at 28 mm³/s where PLA Basic runs at 24. OrcaSlicer’s guide adds that brand and even color change the result within one material.

Temperature also moves the limit. Hotter plastic flows more easily, and Bambu Lab’s wiki suggests raising the nozzle 5 to 10 °C when printing close to the limit. It treats this as a last resort, after checking for under-extrusion and weak layers, because too much heat brings stringing and drooping overhangs. Each profile value holds only at the temperature in that profile, 220 °C for both PLA profiles above.

To find your own number, run OrcaSlicer’s Max volumetric speed test. It defaults to 5 to 20 mm³/s in steps of 0.5. Measure the height where the print starts to fail and work out start + height × step. A failure at 19 mm gives 5 + 19 × 0.5 = 14.5 mm³/s, which becomes about 11.6 to 13 mm³/s after the 10 to 20% margin.

Where to enter max volumetric speed in Bambu Studio and OrcaSlicer

Open the filament preset for editing, stay on the Filament tab and scroll to Volumetric speed limitation. The field is “Max volumetric speed”, in mm³/s. It belongs to the filament, not the printer, so every filament preset carries its own value. Bambu Studio presets for dual extruder variants hold one value per variant.

After slicing, switch the preview’s color scheme to Flow to see where the cap is reached. If a print runs slower than its speed settings suggest, Bambu Lab’s wiki says to check this limit. Both slicers cut the speed of any line that would need more flow than the filament allows.

Filament feed rate

Each mm/s of 1.75 mm filament carries 2.405 mm³/s of plastic, and each mm/s of 2.85 mm filament carries 6.379 mm³/s. So 18 mm³/s needs 7.48 mm/s of 1.75 mm filament into the extruder, or 2.82 mm/s of 2.85 mm filament. To check that the extruder feeds the length of filament the firmware asks for, use the e-steps calculator. For how flow sets the length of a whole job, see the print time calculator.