STL ↔ OBJ Converter

STL stores only triangle geometry — it’s the standard for 3D printing. OBJ also stores geometry but supports vertex normals, texture coordinates, and material references. OBJ is more common in animation, gaming, and engineering visualization. Converting STL → OBJ adds no new information; converting OBJ → STL discards materials and textures.

No. Both formats store geometry as triangle meshes, so the shape is preserved exactly. OBJ → STL drops any materials/textures (STL doesn’t support them). STL → OBJ writes vertex normals computed from the triangle data.

Binary STL files are typically 5–6× smaller than ASCII and parse much faster. ASCII STL is human-readable, which is occasionally useful for debugging, but for any practical use — slicing, sharing, importing into CAD — binary is the standard.

Different 3D software uses different conventions for which axis is “up”. Web 3D formats and three.js use Y-up. CAD and BIM tools like Revit, AutoCAD, FreeCAD, and SolidWorks use Z-up. STL and OBJ files exported from these tools carry Z-up coordinates, which appear rotated when loaded into a Y-up viewer. Use the “Source up axis” toggle in the file info panel to switch — your model will display upright in the preview, and the exported file will be saved in standard Y-up orientation.

Open your browser’s Network tab (F12) and try a conversion. You’ll see zero outbound requests during the conversion itself. Everything runs in JavaScript on this page. The only network traffic is loading the page and the three.js library, both of which happen before you select a file.

This converter handles single .obj files (geometry only). When converting to STL, materials are discarded anyway — STL doesn’t support them. If you need to preserve materials/textures for another OBJ-to-OBJ workflow, use a desktop tool like Blender or FreeCAD.