Extrusion Multiplier & Flow Rate Calculator

Calibrate your extrusion multiplier (flow rate) from a single-wall test print for dimensionally accurate walls and solid top layers.

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Prerequisite: Calibrate your E-Steps first. Flow rate compensates for filament and slicer differences — it cannot fix incorrect extruder mechanics. Use our E-Steps Calculator if you haven't done this yet.

How to Measure

Print a hollow cube (20–30 mm) with 1 perimeter, 0% infill, and 0 top layers. This gives you an open box whose walls you can measure directly.
Measure the wall thickness with calipers near the top of the print (to avoid elephant's foot). Measure all 4 sides and average the results.
Enter your slicer's line width and number of walls below. The target wall thickness is calculated automatically (0.4 mm × 1 = 0.40 mm).

Measurements

Slicer Line Width (mm)

Number of Walls

Measured Wall Thickness (mm)Average of caliper readings

Current Flow Rate (%)Your slicer's current value

New Flow Rate

Update Slicer To

88.89%

Target Thickness0.40 mm

Wall Error+0.050 mm (over-extruding)

Set this as Extrusion Multiplier in PrusaSlicer / OrcaSlicer, or Flow in Cura. This is a per-filament setting — save it in your filament profile.

Why Flow Rate Matters

Flow Rate (or Extrusion Multiplier) scales how much plastic the printer extrudes relative to what the slicer calculated. A value of 100% means "extrude exactly as planned."

Even when your E-Steps are perfectly calibrated (mechanical extruder accuracy), different filaments need different flow rates. This is because filament diameter varies between manufacturers (1.75 mm nominal might be 1.72–1.78 mm in practice), and different materials have different melt characteristics.

Over-extrusion (walls too thick): Parts don't fit together, nozzle drags through top surfaces causing scarring, and blobs appear on outer walls.
Under-extrusion (walls too thin): Weak layer adhesion, gaps in top surfaces, and parts that snap easily along layer lines.

Step-by-Step Calibration

1. Print a Hollow Cube

Slice a 20–30 mm calibration cube with 1 perimeter (wall), 0% infill, and 0 top layers. Using a single wall makes measurement straightforward — the wall thickness should equal your slicer's line width.

2. Note Your Line Width

Check your slicer for "Line Width" or "External Perimeter Width." Common values for a 0.4 mm nozzle are 0.40–0.45 mm. PrusaSlicer defaults to 0.45 mm, Cura defaults to 0.4 mm.

3. Measure Carefully

Use digital calipers to measure wall thickness near the top of the print (avoiding the first few layers where elephant's foot distorts dimensions). Measure all 4 sides and average the readings.

4. Apply the Result

Enter the numbers above. Set the result as your Extrusion Multiplier in PrusaSlicer/OrcaSlicer, or Flow in Cura. Save it in your filament profile — each filament brand and material needs its own value.

Tips & Diagnosis

Top Surface Check

Print a small flat object with 100% top infill. If the nozzle digs ridges into the top surface, flow is too high. If you see gaps between lines where the layer below shows through, flow is too low.

Typical Ranges

Most well-calibrated printers end up between 92–100% flow rate. Values far outside this range usually indicate a different problem (wrong filament diameter setting, clogged nozzle, or uncalibrated E-steps).

Per-Filament Setting

Flow rate varies between filament brands and even between colors from the same manufacturer. Measure once per spool type and save it in your slicer's filament profile for consistent results.

Mechanical Parts

If you are printing parts that need to fit together (like a snap-fit lid or bearing housing), dialing in flow rate is essential. Even a 3% error compounds across multiple walls and ruins tolerances.

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