Convert OBJ to STL in your application
3D InterOp is a CAD interoperability SDK that lets your software read OBJ files and write STL, carrying the mesh data across without re-tessellating it.
Spatial does not offer an online converter or a desktop conversion app. 3D InterOp is a component that software vendors embed in their own products.
- Reads OBJ · Writes STL
- Triangle mesh → triangle mesh
- C++ / C# APIs
OBJ to STL at a glance
Both formats store triangles, so the facets carry over without re-tessellation. The differences are in structure, appearance and metadata.
| OBJ (source) | STL (target) | |
|---|---|---|
| Full name | Wavefront OBJ | Stereolithography |
| Standard / owner | Open format | Open format |
| File extensions | .obj | .stl |
| Geometry | Polygon mesh | Triangle mesh |
| Assemblies / structure | No assembly hierarchy | No |
| 3D InterOp support | Read and write | Read and write |
What's preserved, what changes
Here is what your application can expect to carry across from OBJ to STL.
-
Preserved
Mesh dataThe OBJ facets are read and written to STL without being re-tessellated.
Why software vendors add OBJ to STL conversion
Additive manufacturing
STL is still the input most slicers and print services expect. Writing it lets your users send parts to print directly.
Mesh-based processing
Inspection, scan comparison and mesh-editing tools work on triangles. A mesh output gives them a model they can open anywhere.
Lightweight sharing
A mesh is simpler than the native CAD file and needs no CAD system to open.
Things to check before you ship
- Supported OBJ input: any OBJ version.
- Test tessellation settings on your heaviest parts: finer meshes mean larger files.
- Validate a sample of translated files in the target system your users actually work with.
Working with Spatial was a real milestone for us: Thanks to the powerful 3DInterOp library, we were able to successfully bring our complex CAD-based solutions to the cloud while remaining flexible to meet individual customer requirements. For us, Spatial is not just a technology partner, but a true enabler of our product strategy.
Dr. Arno Michelis, Founder, Simus Systems
Read the Case StudyAbout the formats
-
Source format
What is an OBJ (.obj) file?
OBJ is a simple, widely supported text format for polygon meshes, created by Wavefront. It describes vertices, faces and texture coordinates, with materials in a separate .mtl file.
-
Target format
What is an STL file?
STL describes a 3D surface as a set of triangles, with no units, materials or assembly structure. Its simplicity makes it the usual input for 3D printing.
Frequently asked questions
No re-tessellation is needed. 3D InterOp reads the OBJ facets as visualization data and writes them to STL.
No. STL stores triangles only, with no units, colors or textures. Agree on the unit with the application that reads the file; the 3D InterOp STL reader assumes millimeters.
Yes. 3D InterOp reads the visual material properties of OBJ files on import.
3D InterOp reads any OBJ version, as visualization data.
Yes. 3D InterOp reads and writes both formats, so STL to OBJ is supported too.
-
Building software that needs to convert OBJ to STL?
3D InterOp is an SDK that lets your application read OBJ and write STL alongside 30+ CAD and BIM formats.