STL file converter

The converter turns OBJ, GLB, glTF, PLY and 3MF files into STL, and STL into OBJ, GLB, PLY or 3MF, in your browser. Drop the file, check that the size reads right in millimetres and that the model stands upright, then download. Nothing is uploaded.

What converts and what does not

Every format here describes a shape as triangles, so the shape itself always converts exactly. The differences are in what each format can carry alongside it.

STL has no standard way to store colour, as the Library of Congress format description notes, so colours, materials, textures and animation stop at STL. Parametric history from CAD never makes it into any of these mesh formats: keep your CAD file as the master and export again when the design changes.

Units: the usual reason a converted file is the wrong size

STL, OBJ and PLY files hold bare numbers. The OBJ specification never mentions units, and slicers simply read STL numbers as millimetres. glTF is different: its specification says all distances are in metres, with +Y up. 3MF writes its unit into the file, millimetres by default.

So the converter reads STL, OBJ and PLY as millimetres, GLB as metres and 3MF in whatever unit it declares. When a model would measure less than half a unit across, it is read as metres instead, and the note under Units says so. Always glance at the size readout before downloading: an 80 mm vase should read 80, not 0.08 or 80,000.

Up axis: why models arrive lying down

Slicers treat Z as up. glTF uses Y as up, and the OBJ format does not say which way is up at all, so the converter starts OBJ files at Y up like glTF. It stands Y-up files upright for STL, 3MF and PLY, and turns them back to Y up for GLB, or to the axis you choose for OBJ. If the preview shows the model on its side, switch Up axis under Your file.

Several files, one project

Drop several files together and each becomes a part with its own checkbox. Files sit side by side, 5 mm apart, so they do not overlap; parts from one file keep their positions. Download one merged STL, one STL per part in a zip, or one 3MF with every part as its own object. Each part also gets an edge check: if it has holes, fix it with the STL repair tool before slicing.

Other ways to convert

1. Blender: import with File > Import/Export > Wavefront (.obj), glTF 2.0 (.glb, .gltf) or Stl (.stl), then export the other format from the same menu. The STL exporter has Scale and Scene Unit options, which matter if your scene is not in millimetres. Menu names come from the Blender manual.
2. PrusaSlicer: it imports 3MF, STL, STEP, OBJ and AMF. Use File > Export > Export Plate as STL/OBJ, or File > Save Project as for a 3MF, as Prusa's help center describes.
3. Bambu Studio: File > Import > Import 3MF/STL/STEP/SVG/OBJ/AMF, then save the project, which Bambu Studio stores as a 3MF.

Upload converters also work, but your file goes to someone else's server. For single formats there are focused pages: OBJ to STL, STL to OBJ, GLB to STL and 3MF to STL.