SlicerDial

Max volumetric speed: test the melt limit, then convert mm³/s into mm/s

Published October 15, 202612 sources

Short answer

OrcaSlicer's test prints a tower whose flow rises with height; the limit is start + measured height × step, so 5 + 19 × 0.5 = 14.5 mm³/s with the default settings [1]. To turn flow into speed, divide it by the line's cross-section, h × (w − h × (1 − π/4)) in the Slic3r-family flow model [5]. OrcaSlicer suggests printing 10–20% below the measured value, because the test is a best case [1].

What the limit is and where the slicer applies it

Max volumetric speed is the volume of filament a hotend can melt and push out each second. OrcaSlicer’s filament_max_volumetric_speed caps print speed whenever a feature would demand more flow than that, and the field cannot be zero [2]. PrusaSlicer has the same idea in two places: a filament-level Max volumetric speed where zero means no limit, and an experimental print-level setting for the extruder’s maximum; the effective cap is the lower of the two [6]. OrcaSlicer also carries an experimental, developer-mode Adaptive volumetric speed option imported from Bambu Studio; when enabled, flow is limited by the smaller of a value fitted from line width and layer height and your own maximum [2].

The value belongs to a combination, not to a filament alone. OrcaSlicer lists material, machine, nozzle diameter and extruder setup as factors, and notes that brand and even color can shift it [1]. It also recommends running a temperature tower first and moving toward the top of the filament’s range if you want more flow [1]. Its calibration order places this test after temperature and before pressure advance [4].

Running OrcaSlicer’s test

  1. Open the max volumetric speed test. OrcaSlicer recommends the defaults of 5 mm³/s start, 20 mm³/s end and a 0.5 step unless you already know roughly where the limit sits.
  2. Slice and print. The tower’s flow rises steadily with height.
  3. Find where layers start to fail or quality drops. A change in sheen from glossy to matte is often the first visual sign.
  4. Measure the height just below the defects with calipers or a ruler.
  5. Compute start + height × step. The wiki’s example: 19 mm gives 5 + 19 × 0.5 = 14.5 mm³/s.
  6. Alternatively, open the Preview with the Flow color scheme, move to the measured height and read the flow from the toolhead slider.
  7. Enter the result in the filament settings.

Steps and defaults are from OrcaSlicer’s guide [1]. It calls the result a best case that ignores retraction and other settings that can provoke clogs, and suggests reducing it by 10–20% or more for quality and strength. Taking 15% off the example gives 14.5 × 0.85 ≈ 12.3 mm³/s.

Bambu Studio’s developer-mode Max Flowrate test for third-party printers uses the same formula. Bambu Lab’s example uses a start of 10 and a step of 1 with failure at 14 mm, so 10 + 14 × 1 = 24 mm³/s, and suggests a more modest 5–10% reduction [8]. The two vendors’ margins differ; OrcaSlicer ties its larger margin to print quality and strength.

From mm³/s to mm/s

PrusaSlicer computes the cross-section of a normal extrusion as a rectangle with semicircular ends: area = h × (w − h × (1 − π/4)), with layer height h and line width w in millimeters. Bridges are treated as a circle of diameter w, π × w² / 4 [5]. OrcaSlicer states that it follows the same Slic3r oval model [3]. Maximum speed is then volumetric limit ÷ area.

Line width × layer height Cross-section (mm²) Speed at 12.3 mm³/s Speed at 24 mm³/s
0.42 × 0.20 mm 0.0754 163 mm/s 318 mm/s
0.45 × 0.20 mm 0.0814 151 mm/s 295 mm/s
0.45 × 0.28 mm 0.1092 113 mm/s 220 mm/s
0.62 × 0.30 mm 0.1667 74 mm/s 144 mm/s

The table is arithmetic from the formula above. It shows why the same filament limit allows very different speeds: thicker layers and wider lines move more plastic per millimeter, so the cap bites at lower speeds. The volumetric speed calculator does the conversion in both directions.

Klipper has a separate safety check, max_extrude_cross_section, which rejects moves whose extrusion cross-section exceeds a limit that defaults to 4 × nozzle_diameter² [7]. It guards against runaway extrusion on small moves and is not a melt-rate limit.

What hotend makers publish

Hotend ratings are a ceiling for any filament on that hardware; the filament’s own limit may be lower. Two manufacturers publish figures for specific materials:

Hotend, nozzle PLA PETG Other
Bambu Standard Flow, 0.4 mm 24 mm³/s (PLA Basic), 28 (PLA Matte) 24 (PETG HF)
Bambu High Flow, 0.4 mm 40 (PLA Basic), 48 (PLA Matte) 32 (PETG HF)
Bambu High Flow, 0.6 and 0.8 mm 40 40
E3D Revo brass, 0.4 mm 13 at 220 °C 17 at 240 °C ASA 15 at 260 °C
E3D Revo High Flow brass, 0.4 mm 16 at 220 °C 27 at 240 °C ASA 26 at 260 °C

Bambu values are from the High Flow Hotend product page [10]; E3D values are from its Revo support pages [11, 12]. Bambu Lab adds that its High Flow Hotend gives no flow gain on A1/A2-series printers [10]. E3D lists a temperature beside every figure, which matters: in its own tables PETG at 240 °C out-flows PLA at 220 °C on the same nozzle. Treat each table as valid only for the stated conditions. Filament makers’ own figures, where published, are collected on the max volumetric speed chart.

Signs you are above the limit

OrcaSlicer warns that printing at high volumetric speed can cause poor layer adhesion and nozzle clogs, and describes the filament cap as protection against clogs, under-extrusion and weak layers [1, 2]. Because the cap applies to whatever feature demands the most flow, fast, thick features such as sparse infill reach it first. If under-extrusion appears only at speed, lowering the volumetric cap is a more targeted fix than raising flow ratio.

Changing the limit has a knock-on effect: Bambu Lab lists a change to max volumetric speed as a reason to recalibrate flow dynamics [9], so re-run the pressure advance test afterwards. Fast-printing filaments marketed for high flow are covered in the high-speed PLA guide.

Questions

Why does the same PLA test differently on two printers?

OrcaSlicer says the limit depends on the material, machine, nozzle diameter and extruder setup, and that even brand and color can change it, so it should be calibrated per printer and filament [1].

Does a high-flow hotend raise the limit on every printer?

Not necessarily. Bambu Lab states its High Flow Hotend fits A1/A2-series printers but performs the same as the standard hotend there [10].

Sources

  1. Max Volumetric Speed (FlowRate) Calibration. OrcaSlicer Wiki. Slicer documentation. Defaults 5-20 mm³/s step 0.5, formula, example, 10-20% margin, temperature tip. Accessed October 12, 2026.
  2. Material Volumetric Speed Limitation. OrcaSlicer Wiki. Slicer documentation. filament_max_volumetric_speed definition; adaptive volumetric speed. Accessed October 12, 2026.
  3. Precision (quality settings). OrcaSlicer Wiki. Slicer documentation. OrcaSlicer follows Slic3r's oval extrusion model. Accessed October 12, 2026.
  4. Calibration Guide. OrcaSlicer Wiki. Slicer documentation. Volumetric speed after temperature, before pressure advance. Accessed October 12, 2026.
  5. Flow.cpp (Flow::mm3_per_mm). Prusa Research, PrusaSlicer source on GitHub. Source code. Cross-section h × (w − h × (1 − π/4)); bridges use π·w²/4. Accessed October 12, 2026.
  6. ConfigDefsFDM.cpp (setting definitions and tooltips). Prusa Research, PrusaSlicer source on GitHub. Source code. Filament and print Max volumetric speed settings. Accessed October 12, 2026.
  7. Configuration reference. Klipper documentation. Firmware documentation. max_extrude_cross_section default 4 × nozzle_diameter². Accessed October 12, 2026.
  8. Calibration for 3rd Party Printer. Bambu Lab Wiki. Manufacturer documentation. Bambu Studio Max Flowrate test, formula, 5-10% margin. Accessed October 12, 2026.
  9. Flow Dynamics Calibration. Bambu Lab Wiki. Manufacturer documentation. Recalibrate flow dynamics after changing max volumetric speed. Accessed October 12, 2026.
  10. Bambu High Flow Hotend - H2/P2S/X2D. Bambu Lab (US store). Product page. Max volumetric speed table for standard and high-flow hotends; A1/A2 note. Accessed October 12, 2026.
  11. Revo Support: Brass Nozzle. E3D. Manufacturer documentation. Maximum volumetric flow rates by nozzle size, material and temperature. Accessed October 12, 2026.
  12. Revo Support: High Flow Brass Nozzles. E3D. Manufacturer documentation. Maximum volumetric flow rates for Revo High Flow nozzles. Accessed October 12, 2026.