How to use it
- Choose Flow or Max volumetric flow and speed.
- For flow: print a single-wall cube, measure the wall and enter it.
- For speed: enter layer height, line width, speed and your hotend's flow limit.
- Copy the new value into your slicer profile.
Flow rate (extrusion multiplier) calibration
Flow fine-tunes how much plastic the slicer asks for, per filament. Even with correct e-steps, filaments differ slightly in diameter and how they melt, so a flow of 92–100% is common.
new flow = old flow × expected wall ÷ measured wall
The expected wall is your line width in a single-wall (vase mode) test print. Example: flow 100%, line width 0.45 mm, measured wall 0.48 mm (average of four sides):
100 × 0.45 ÷ 0.48 = 93.75%, or 0.938 as a multiplier.
OrcaSlicer and Bambu Studio call this setting flow ratio, PrusaSlicer extrusion multiplier, Cura flow.
How to measure the test wall
- Calibrate e-steps first.
- Print a 20 mm cube in vase mode (spiral, one wall, no top) with the line width you normally use.
- Measure each side with calipers in the middle of the wall, away from the seam and corners.
- Average the four readings and enter the result.
A difference of just 0.02 mm on a 0.45 mm wall is already 4–5%, so measure carefully. Many slicers also include their own flow test patterns; the formula here is handy when you prefer the classic wall method or want to double-check.
Volumetric flow: how fast can you print?
Every hotend can melt only so much plastic per second. That limit is the max volumetric speed, in mm³/s:
volumetric flow = layer height × line width × print speed
At 0.2 mm layers, 0.45 mm lines and 100 mm/s, the hotend must melt 0.2 × 0.45 × 100 = 9 mm³/s. The calculator also shows how fast the filament itself moves through the extruder for that flow.
Enter your hotend's limit and you get the maximum speed for your settings and for common layer heights. With a 15 mm³/s limit and 0.45 mm lines, that is about 167 mm/s at 0.2 mm layers and about 104 mm/s at 0.32 mm layers.
Typical flow limits
| Hotend type | Approximate max flow (PLA) |
|---|---|
| Standard V6-style hotend | about 10–15 mm³/s |
| Volcano-style or similar long melt zone | about 20–30 mm³/s |
| High-flow hotends | 30 mm³/s and up |
These are rough ranges; the real number depends on temperature, nozzle size and filament. Measure your own with a max flow test (extrude at increasing speeds until it starts to underextrude), and set a slightly lower value in your slicer's Max volumetric speed so it slows down automatically on wide or thick lines.
Signs you are over the limit
If you ask for more than the hotend can melt, you will see underextrusion that gets worse on long straight moves, weak layer bonding, a clicking extruder, or a skipping gear. The calculator warns you when the requested speed needs more flow than your limit and suggests the maximum speed instead. Raising the temperature a little or switching to a high-flow nozzle can help, but at some point the only fix is to slow down. Remember that infill and first layers often use wider lines or thicker layers than walls, so they hit the limit first. All calculations run in your browser.
Frequently asked questions
What is extrusion multiplier?
A slicer setting that scales the amount of plastic extruded. 1.0 (100%) means exactly what the slicer calculated; 0.95 means 5% less.
How do I calculate the new flow rate?
Multiply the old flow by the expected wall thickness and divide by the measured wall thickness from a single-wall test print.
What is max volumetric speed?
The most plastic your hotend can melt per second, in mm³/s. Above it, prints underextrude no matter what the speed setting says.
How do I calculate volumetric flow?
Layer height × line width × speed. For example, 0.2 × 0.45 × 100 mm/s = 9 mm³/s.
Should flow be set per filament?
Yes. Calibrate e-steps once per printer, then set flow in each filament profile.
Last updated: November 12, 2026