If your phone stand shows up in PrusaSlicer or Cura as a speck—or as a giant slab—the slicer is usually fine. The problem is almost always how Blender stores units and whether you applied scale before export. STL has no unit metadata. The numbers you send are raw mesh coordinates. Get the studio setup right once, apply scale every time, and check the mesh is manifold before you hit Export.
This page is the BlenderZen default for printable parts: Metric, unit scale 0.001, millimetres on screen, then Ctrl+A → Scale, then a short 3D Print Toolbox pass. It is written for beginners who already own a printer (or use a print service) and want the next STL to arrive at the right size.
The studio default for printable parts
For FDM and resin parts, use one setup and stick to it: Scene Properties → Units → Unit System: Metric; Unit Scale: 0.001; Length: Millimeters. With unit scale at 0.001, the grid and the Item dimensions in the N-panel read in millimetres. That matches how most slicers treat unitless STL numbers: one Blender millimetre becomes one millimetre in the slicer when export scale is left at 1. Changing unit scale does not resize existing mesh. It only changes how numbers display. After you switch, remodel or scale geometry to real millimetre sizes, then apply that scale with Ctrl+A → Scale. Keep one unit system for the whole file.
[SCREENSHOT: Scene Properties → Units panel showing Metric, Unit Scale 0.001, Length Millimeters]
Houses vs parts: do not mix systems in one file
Architectural walkthroughs and room layouts often live in metres: unit scale 1.0 and Length Meters. Printable grips, brackets, and phone stands live in millimetres with unit scale 0.001. Mixing both in one .blend is a common failure. Use metres for rooms, houses, and camera walkthroughs; use millimetres plus unit scale 0.001 for small printed objects. If a printed part must enter a metre-scale scene, apply scale on the part first, then convert deliberately with a known rule.
Apply scale before every STL
Resizing with S in Object Mode changes transform scale while mesh data underneath can still be the old size. Before every STL export, select the object, press Ctrl+A → Scale, confirm Item → Scale reads 1, 1, 1, and check N-panel Item → Dimensions against the real-world millimetre size. STL files do not store units, so fix the Blender file instead of relying on silent slicer rescaling.
Run this checklist every time you export: confirm N-panel dimensions, confirm scale 1, 1, 1, apply final-solid modifiers, leave export Scale at 1 with the scene already Metric + 0.001 + millimetres, and verify one export in the slicer. Avoid stacking Apply Scene Unit conversion factors.
[SCREENSHOT: Item panel Scale 2,2,2 vs after Ctrl+A → Scale 1,1,1]
Export checklist
Run this export checklist every time: confirm N-panel dimensions match the real-world millimetre size; confirm scale is 1, 1, 1 using Ctrl+A -> Scale; apply final-solid modifiers; with Metric, unit scale 0.001, and millimetres already set, leave STL export Scale at 1; avoid stacking scene-unit conversion factors; and verify one export in the slicer.
[SCREENSHOT: Same part dimensions in Blender N-panel vs slicer after correct export]
Next step
ScaleIt is for orthographic cameras and paper sizes when you plot drawings—not for fixing FDM or resin STL export size. For printable parts, use this page and the 3D Printing course. For paper or orthographic layouts, see ScaleIt: https://blenderzen.gumroad.com/l/ScaleIt.
Glance at wall thickness for your nozzle and material. Thin walls should be intentional, not accidental. A manifold, watertight model has every edge shared by exactly two faces: no holes, loose edges, or T-junctions. These checks catch failures before you waste filament or resin.
ScaleIt is for orthographic cameras and paper sizes when you plot drawings—not for
ScaleIt is for orthographic cameras and paper sizes when you plot drawings—not for fixing FDM or resin STL export size. For printable parts, use this page and the 3D Printing course. For scaling models to paper or orthographic layouts, see ScaleIt at https://blenderzen.gumroad.com/l/ScaleIt.
Studio default in one line: Metric – unit scale 0.001 – millimetres – apply scale – manifold check – STL at export scale 1.
Take the 3D Printing course on Udemy: https://www.udemy.com/course/learn-3d-printing/?referralCode=7A81C7D340298F183183
More BlenderZen courses: https://blenderzen.com/courses/
[SCREENSHOT: 3D Print Toolbox Solid / non-manifold result – clean vs broken]
