FDM Retraction in mm Calculator

3D Printing Retraction Settings

During travel moves, when nothing is being printed, the extruder pulls the filament back a little so molten plastic doesn't dribble out of the nozzle. Skip that and you end up with stringing (those thin strands stretched between parts) plus blobs and zits all over the surface. The pull-back distance is in millimeters, and what mostly sets it is the kind of extruder you have: distance = base_value × nozzle_factor.

On a Bowden extruder, the motor sits far from the hotend and the filament runs through a PTFE tube. That long run between the drive gear and the nozzle compresses the filament, and you have to relieve it, so retraction usually lands around 4–6 mm. A direct drive extruder mounts the motor right on the hotend, so the path is short and stiff and 0.5–2 mm does the job. Speed normally sits between 30–60 mm/s. Go too fast and you grind the filament; too slow and it keeps oozing.

Applications

Hobbyists and pros reach for this when they break in a new filament (PLA, PETG, ABS, TPU), dial in a slicer profile (Cura, PrusaSlicer, OrcaSlicer, Bambu Studio), run multi-part models full of travel moves, or chase down stringing. The usual way to calibrate is the retraction tower test: it prints a tower with two pillars, bumping the retraction distance up as it climbs, so you can eyeball where it stops stringing.

FAQ

Why does TPU need almost no retraction? Flexible filaments like TPU squish when you yank them back and can buckle inside the extruder, so keep it to 0–1 mm and print slower.

Does nozzle diameter affect retraction? A bit. Bigger nozzles (0.6–0.8 mm) carry more melt and can want a touch more retraction, while smaller ones (0.2–0.3 mm) tolerate less.

What if I still get stringing after calibration? Drop the nozzle temperature 5–10°C, turn on Z-hop, push travel speed up to 150–200 mm/s, and make sure the filament is dry. Moisture is the #1 hidden cause of stringing.