Convert STP to 3MF in your application
3D InterOp is a CAD interoperability SDK that lets your software read STP files and write 3MF, generating the 3MF mesh from the geometry it reads, with tessellation settings your application controls.
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 STEP · Writes 3MF
- Exact geometry → triangle mesh
- C++ / C# APIs
STP to 3MF at a glance
STEP stores exact geometry; 3MF stores triangles. The translation is a tessellation, and the settings you choose decide how close the mesh stays to the original.
| STEP (source) | 3MF (target) | |
|---|---|---|
| Full name | Standard for the Exchange of Product model data | 3D Manufacturing Format |
| Standard / owner | ISO 10303 — AP203, AP214, AP242 | 3MF Consortium, ISO/IEC 25422 |
| File extensions | .stp, .step | .3mf |
| Geometry | Exact B-Rep | Triangle mesh |
| Assemblies / structure | Yes | Objects and build items |
| PMI | Graphical and semantic (AP242) | None |
| 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 STEP to 3MF.
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Improved
Healed geometry3D InterOp repairs and heals STEP data during translation.
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Changes
Geometry is tessellatedThe exact STEP B-Rep is replaced by a triangle mesh, generated by 3D InterOp from the exact geometry it reads. Accuracy depends on the tessellation settings your application uses.
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Changes
Assembly structure3MF has no native assembly hierarchy. Decide in your application how STEP product structure is grouped or flattened before writing.
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Not carried
PMI3MF has no place for PMI, so the PMI read from STP isn’t written.
Why software vendors add STP to 3MF conversion
Additive manufacturing
3MF 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
- Written 3MF versions: 3MF 1.1.
- The 3MF writer is available through the UConnect interface only.
- Supported STP input: AP203, AP214 and AP242.
- 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
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Source format
What is a STEP (.stp) file?
STEP is the ISO 10303 standard for exchanging 3D product data between CAD systems. Its application protocols range from exact geometry (AP203, AP214) to full model-based definition with PMI (AP242).
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Target format
What is a 3MF (.3mf) file?
3MF is an open format for additive manufacturing, defined by the 3MF Consortium. It stores triangle meshes with units, colors and build information in a single package.
Frequently asked questions
3D InterOp tessellates the geometry it reads from STP when it writes 3MF. Your application sets the tolerances, so it controls the trade-off between accuracy and file size.
3MF has no place for PMI, so the PMI read from STP isn’t written. Your application can still access it after import, or offer STEP AP242 as an output.
3MF has no assembly hierarchy, so your application decides how the STP structure is grouped or flattened before writing.
The 3MF writer is available through the 3D InterOp UConnect interface.
3D InterOp reads AP203, AP214 and AP242.
3D InterOp writes 3MF 1.1.
Yes. 3D InterOp reads and writes both formats, so 3MF to STP is supported too.
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Building software that needs to convert STP to 3MF?
3D InterOp is an SDK that lets your application read STEP and write 3MF alongside 30+ CAD and BIM formats.