Guide · Measurement tools
Flow ratio and max volumetric speed: calibrate in the right order
The calibration order, choosing a temperature, OrcaSlicer's flow ratio and max volumetric speed tests, why to derate 10-20%, and what outside measurements show.
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Short answer
Calibrate in order: extruder first, then pressure advance, then flow ratio for each filament. Find max volumetric speed with a slicer test, then derate it by 10-20% or more, because the test shows a best case. Outside measurements show under-extrusion can start well before the extruder audibly skips.
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- Clockwise Tools DPIR‑0105 IP65 digital indicator, 0‑1 in / 25.4 mmCheck price on Amazon
- VINCA DMCA‑0105 IP64 digital outside micrometer, 0‑1 in / 0‑25 mmCheck price on Amazon
The order
Each step assumes the one before it is right:
- Extruder calibration: E-steps or rotation distance. See E-steps and rotation distance.
- Temperature for the filament.
- Pressure advance. See pressure advance and Linear Advance.
- Flow ratio per filament.
- Max volumetric speed per filament.
The ellis3dp.com guide treats extruder calibration as separate from extrusion multiplier, which it says should be tuned at least per filament brand and type, after extruder calibration and pressure advance.[1] It adds that the multiplier may also vary by color or spool.
Choosing a temperature
OrcaSlicer's temperature tower guidance says to pick the middle of the range that prints well, leaning higher for faster or higher-flow printing.[2] Lower temperatures typically reduce stringing; higher temperatures generally improve layer adhesion.
Flow ratio: judge the top surface
OrcaSlicer's flow ratio calibration is tied to the selected filament profile, and is judged by choosing the test block with the smoothest top surface.[3] On Bambu Lab printers, OrcaSlicer says not to select the built-in "Flow calibration" option for this test.
The ellis3dp.com guide also prefers a visual and tactile top-surface method, in 1-2% then 0.5% steps.[1] It argues that measuring thin walls with calipers is unreliable, because layer wobble and filament variation inflate the reading.[4] The calipers guide explains why.
Max volumetric speed: a best case
Max volumetric speed caps how many mm³ of plastic per second the slicer will ask for. OrcaSlicer's test calls its result a best-case scenario and suggests reducing the measured value by 10-20% or more for print quality and strength.[5] It notes that brand and color can significantly change max flow within one material, and that high volumetric speed can cause poor layer adhesion or clogs.
What outside measurements show
| Setup | Result | Source |
|---|---|---|
| E3D V6 with Bondtech gears, Prusa MK3S, PLA at 215 °C (2020) | About 3% under-extrusion at 9 mm³/s; audible skipping from 15 mm³/s | [6] |
| Near-stock Ender-3 Pro, PLA (2022) | About 6 mm³/s at 200 °C, 8 at 220 °C, 12 at 240 °C | [7] |
Both are CNC Kitchen's, each one printer and one filament. The MK3S result shows under-extrusion beginning before the extruder skips, which is why a test that ends at the first skip overstates usable flow. The author put that setup's practical limit at about 10-15 mm³/s at 215 °C.[6] The Ender-3 Pro result shows temperature mattering, and the author notes higher temperature brings more stringing, blobs, emissions and possible degradation.[7]
Why the melt is not simply the setpoint
A 2023 study in Rapid Prototyping Journal, hosted on NIST's site, found that measured melt temperature and its variation depend on flow rate, hotend setpoint and nozzle diameter, and that heat loss to the air had a significant effect.[8] It used thermography and a model on one custom hotend, so it is not a benchmark of consumer hotends. It does explain why the same setpoint can behave differently at different flows.
Next
Questions
How do I find my hotend's max flow?
Run your slicer's max volumetric speed test with the filament you will use. OrcaSlicer's version calls its result a best case, so reduce the number before you use it.[5]
Why derate the max volumetric speed result?
OrcaSlicer suggests reducing the measured value by 10-20% or more for print quality and strength, and notes that high volumetric speed can cause poor layer adhesion or clogs. In CNC Kitchen's 2020 MK3S test, under-extrusion of about 3% began at 9 mm³/s, well before audible skipping at 15.[5][6]
What order should I calibrate in?
Extruder calibration (E-steps or rotation distance) first, then pressure advance, then flow ratio per filament. The ellis3dp.com guide puts extrusion multiplier after both.[1]
Does a hotter nozzle mean more flow?
On one near-stock Ender-3 Pro with PLA, CNC Kitchen found usable flow of about 6 mm³/s at 200 °C, 8 at 220 °C and 12 at 240 °C. The author notes that hotter printing also brings more stringing, blobs and emissions.[7]