Convert RFA to STL in your application
3D InterOp is a CAD interoperability SDK that lets your software read RFA files and write STL, generating the STL 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 Revit family · Writes STL
- Mixed geometry → triangle mesh
- C++ / C# APIs
RFA to STL at a glance
Revit family can mix exact solids and facets; STL stores triangles only, so the whole model is tessellated when it is written.
| Revit family (source) | STL (target) | |
|---|---|---|
| Full name | Revit family | Stereolithography |
| Standard / owner | Autodesk | Open format |
| File extensions | .rfa | .stl |
| Geometry | B-Rep and mesh (read); mesh (written by 3D InterOp) | Triangle mesh |
| Assemblies / structure | Nested families; assembly structure written by 3D InterOp | 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 Revit family to STL.
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Changes
Geometry is tessellatedThe exact Revit family 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 structureSTL has no native assembly hierarchy. Decide in your application how Revit family product structure is grouped or flattened before writing.
Why software vendors add RFA 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 RFA input: Revit 2015 to 2026.
- 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 an RFA (.rfa) file?
An RFA file is a Revit family: a reusable component such as a door, a window or a piece of equipment, with its geometry, types and parameters, loaded into Revit projects.
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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
3D InterOp tessellates the geometry it reads from RFA when it writes STL. Your application sets the tolerances, so it controls the trade-off between accuracy and file size.
STL has no assembly hierarchy, so your application decides how the RFA structure is grouped or flattened before writing.
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.
3D InterOp reads Revit 2015 to 2026.
Yes. 3D InterOp reads and writes both formats, so STL to RFA is supported too.
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Building software that needs to convert RFA to STL?
3D InterOp is an SDK that lets your application read Revit family and write STL alongside 30+ CAD and BIM formats.