Flow Rate Calculator (Extrusion Multiplier)
Print a single-wall cube, measure the walls with calipers, and get the flow percentage (Cura, PrusaSlicer) or ratio (Bambu Studio, OrcaSlicer) to type into the filament profile.
The formula
The slicer assumes each wall line comes out exactly as wide as the line width setting. If the wall is thicker than that, the printer is pushing too much plastic and the flow comes down in proportion; thinner, and it goes up. Because it's a ratio, it works whether your slicer shows flow as 100% or 1.00.
Worked example
Cube printed at 0.45 mm line width, 100% flow. Walls measure 0.48, 0.47, 0.49 and 0.48 mm.
- Average: (0.48 + 0.47 + 0.49 + 0.48) ÷ 4 = 0.480 mm
- New flow: 100% × 0.45 ÷ 0.480 = 93.8% — enter 94 in Cura, or 0.938 in Bambu Studio, OrcaSlicer or PrusaSlicer
Printing the test cube
- Slice a 20 × 20 × 20 mm cube (any calibration cube model works, or add a plain cube in the slicer).
- Set 1 wall, 0 top layers, 0% infill. In Cura enable Spiralize Outer Contour; in PrusaSlicer/Orca/Bambu enable Spiral vase. Keep bottom layers — you want the base for stability.
- Use the same line width, layer height, temperature and speed you normally print with. Flow is partly a temperature effect, so calibrate the profile you'll actually use.
- Let it cool completely. Measure each wall with digital calipers about halfway up, squeezing gently — a plastic wall compresses. Take two readings per side if they disagree.
- Enter the four readings above. Apply the new flow, reprint, and expect the walls to land within ±0.02 mm of the set width.
Where flow lives in each slicer
| Slicer | Setting | Form |
|---|---|---|
| Bambu Studio / OrcaSlicer | Filament → Flow ratio | Ratio, e.g. 0.98 |
| PrusaSlicer / SuperSlicer | Filament Settings → Extrusion multiplier | Ratio, e.g. 0.95 |
| Cura | Material → Flow | Percent, e.g. 95 |
| Simplify3D | Extruder → Extrusion Multiplier | Ratio |
| Marlin firmware (temporary) | M221 S95 | Percent — but prefer the slicer, so it travels with the profile |
Set it in the filament profile, not the print profile. Flow is a property of the material and the temperature, and different spools of the same material can differ by a few percent.
Order of operations
Flow interacts with everything upstream of it. Calibrate in this order and each step stays fixed:
- E-steps / rotation distance — once per extruder, so the right length of filament is delivered.
- Flow — this page, once per material.
- Temperature and retraction — with a test tower, per material.
- Dimensional accuracy — scale and hole compensation, per material.
Limits of the single-wall method
A single 0.45 mm wall is thin and can bulge or lean as the print grows, so the measurement scatters more than the underlying flow does. That's why it's four sides averaged and measured mid-height. Two known corrections some people apply: Cura's line width includes the full rounded edge of the extrusion, while some flow tests assume a rectangular cross-section, which shifts results by a couple of percent; and printing the test at high speed will under-read if the hotend can't keep up (check the volumetric flow). If two runs land within 1–2% of each other, stop — that's within the diameter tolerance of the filament itself.
Frequently asked questions
How do I calibrate flow rate?
Print a 20 mm cube with one wall, no top layers, no infill (vase/spiralize mode is easiest) at your normal settings. Measure each wall with calipers near mid-height. New flow = current flow × line width set in the slicer ÷ average measured thickness. So a 0.45 mm line width that measures 0.48 mm means flow should drop to about 94% of what it was.
Is flow rate the same as extrusion multiplier?
Yes. Cura and Bambu Studio call it Flow (Cura in percent, Bambu/Orca as a ratio like 0.98), PrusaSlicer and SuperSlicer call it Extrusion multiplier (a ratio like 0.95), Simplify3D calls it Extrusion Multiplier. They all scale how much plastic is pushed for every line.
Should I calibrate e-steps or flow first?
E-steps first, once per extruder. Flow is then tuned per material and corrects everything e-steps can't: filament diameter tolerance, how the melt spreads at a given temperature, and slicer assumptions. If you tune flow before e-steps you'll be re-doing it.
Is the single-wall method accurate?
It's the classic approach and good to within a couple of percent. Its known weakness is that a single unsupported wall can bulge, so measure at mid-height rather than the top, and take all four sides. OrcaSlicer's built-in flow calibration (pass 1 and 2) prints patches to compare visually and is a good cross-check.
What flow rate is normal?
For PLA, 0.92–1.00 (92–100%). PETG is usually a little lower, 0.90–0.97. ABS/ASA 0.93–1.00. TPU often needs over 100% because it compresses in the extruder. If the calculator wants more than about ±8% from stock, suspect e-steps or an extruder problem rather than flow.
Last reviewed September 7, 2026. Spotted an error or want another calculator? Tell us.