OBJ to STL converter

To convert OBJ to STL, drop the .obj file on the converter above, check that the model stands upright and measures right in millimetres, then download the STL. Every object in the OBJ becomes a part you can merge into one STL or save as separate files. Nothing is uploaded.

What happens to materials, textures and colours

An OBJ file describes the shape. Its colours and textures live elsewhere: the OBJ specification points to a separate material library file with mtllib and assigns materials with usemtl, and that library in turn names image files for textures. STL has no standard way to store colour at all, as the Library of Congress notes, so none of this can come along.

If you want the colours in your print, you have two routes:

• Keep the parts apart. Download STL per part, or convert to 3MF with one object per part, then give each part a filament in your slicer.
• Let the slicer read the colours. Bambu Studio imports colour information from OBJ files and matches it to your filaments. PrusaSlicer ignores OBJ materials and textures on import.

Why OBJ files come in the wrong size or the wrong way up

OBJ stores plain numbers with no unit and no rule about which axis is up. That causes the two classic surprises:

1. Sideways model. Files saved with Y as up land on their back in a slicer, which treats Z as up. The converter assumes Y up for OBJ and stands the model upright. If the preview shows it lying down, switch Up axis to Z up.
2. Wrong size. A file saved in metres reads 1,000 times too small as millimetres. When a model would measure under half a unit across, the converter reads it as metres and says so. Check the size readout, and use Scale to height if you want an exact height.

Objects, groups and polygons

OBJ files name their pieces with o (object) or g (group) lines. The converter makes one part per object; if the file has no objects, one part per group. Faces with four or more corners are split into triangles. Lines and points are skipped, because they have no surface to print.

Check it before you print

Each part gets an edge check after loading. "Watertight" means every edge is shared by exactly two faces, so the slicer sees a closed solid. Models made for games or rendering never had to be closed, so they can have holes or loose faces; if a part shows open edges, fix it in the STL repair tool or check it in the STL viewer.

Other ways to convert

1. PrusaSlicer: import the OBJ (Ctrl+I), then File > Export > Export Plate as STL/OBJ. Steps are in Prusa's help center.
2. Blender: File > Import/Export > Wavefront (.obj) to bring it in, then File > Import/Export > Stl (.stl) to save it. The STL exporter has Scale and Scene Unit options for fixing the size, per the Blender manual.

For other formats, the STL file converter also reads GLB, PLY and 3MF, and the OBJ viewer opens an OBJ without converting it.