This tool calibrates your printer’s extrusion multiplier (also called flow rate or flow ratio) by comparing how thick a single-wall test print should be against how thick it actually measures. The result is a precise multiplier that eliminates systematic over- and under-extrusion on any FDM/FFF machine.
How it works
Print a calibration object with a single perimeter (one wall, 0% infill, no top/bottom layers), so exactly one extrusion line forms each wall. In an ideal world that wall is as thick as the extrusion (line) width you sliced at. In practice it comes out thicker (over-extrusion) or thinner (under-extrusion).
The correction is a simple proportional scaling:
New multiplier = current multiplier x (expected thickness / measured thickness)
If you printed at a flow of 1.00 with a 0.45mm target and your calipers read 0.48mm, you are pushing too much plastic. The new multiplier is 1.00 x (0.45 / 0.48) = 0.9375, i.e. 93.75% flow. Re-slice at that value and the wall lands on target.
Worked example
- Current multiplier: 0.98 (98%)
- Expected wall (line width): 0.40mm
- Measured average: 0.43mm
New multiplier = 0.98 x (0.40 / 0.43) = 0.9116, or about 91.2% flow. The drop reflects that you were over-extruding by roughly 7.5%.
E-steps calibration versus flow rate — which to do first
These two calibrations address different things and must be done in order:
E-steps first. E-steps (or the Rotation Distance in Klipper) tell the extruder motor how many motor steps are required to push exactly 100mm of filament. To check this, mark a length of filament and command the printer to extrude 100mm without the hotend heating. If the measured amount differs from 100mm, the E-steps need adjusting. This calibration is motor-mechanical and is done without printing.
Flow rate second. Once E-steps are correct (the extruder moves the right length), flow rate corrects the deposited volume to account for filament diameter variation, back-pressure in the hotend, and slippage at speed. This calibration requires a test print and calipers. If you adjust flow rate without correct E-steps underneath, your correction will drift every time conditions change slightly.
What over- and under-extrusion look like
| Symptom | Likely cause |
|---|---|
| Rough or bubbly top surface | Over-extrusion — too much material |
| Gaps in top surface or infill | Under-extrusion — too little material |
| Holes in parts undersized | Over-extrusion expanding walls inward |
| Weak layer bonding, splitting | Under-extrusion, layers not fusing |
| Blobs and zits on perimeters | Often over-extrusion combined with retraction issues |
Tips for an accurate measurement
- Print the test wall slowly (around 20–30 mm/s) so pressure-advance and flow lag do not distort the wall.
- Average several caliper readings at different heights; deburr any seam before measuring.
- Use digital calipers and zero them before measuring.
- Re-check flow rate after changing filament brand or material — different polymers and pigments flow differently, and even the same filament from a different spool can vary.
- On Bambu printers the setting is called “Flow Ratio” (default 0.98); in PrusaSlicer it is “Extrusion Multiplier”; in Klipper/Mainsail it may be a pressure-advance or flow factor depending on your setup.