Convert STL to RFA in your application
3D InterOp is a CAD interoperability SDK that lets your software read STL files and write RFA, writing a Revit family (.rfa) as mesh geometry.
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 STL · Writes Revit family
- Triangle mesh → triangle mesh
- C++ / C# APIs
STL to RFA at a glance
Both formats store triangles, so the facets carry over without re-tessellation. The differences are in structure, appearance and metadata.
| STL (source) | Revit family (target) | |
|---|---|---|
| Full name | Stereolithography | Revit family |
| Standard / owner | Open format | Autodesk |
| File extensions | .stl | .rfa |
| Geometry | Triangle mesh | B-Rep and mesh (read); mesh (written by 3D InterOp) |
| Assemblies / structure | No | Nested families; assembly structure written by 3D InterOp |
| 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 STL to Revit family.
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Preserved
Mesh dataThe STL facets are read and written to RFA without being re-tessellated.
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Changes
Geometry written as meshThe Revit writer writes mesh only: exact B-Rep from STL isn’t exported to the family.
Why software vendors add STL to RFA conversion
Bring product content into Revit
Manufacturers publish their products as Revit families so architects can place them in building models. Writing RFA files lets your users produce that content from CAD data.
Coordinate with Revit-based teams
Many building projects are modeled in Revit. A Revit family gives those teams the geometry in a form they can load into their project.
Fewer manual remodeling steps
Without a direct export, CAD parts are often remodeled by hand in Revit. Writing the family directly saves your users that step.
Things to check before you ship
- Written RFA versions: Revit 2026 families (.rfa).
- Revit families are written in millimeters, without Revit parameters.
- Supported STL input: any STL version.
- 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 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.
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Target 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.
Frequently asked questions
No. The Revit writer writes mesh geometry only, without B-Rep or Revit parameters, for the latest Revit version (Revit 2026 in 3D InterOp 2026 1.0.1).
No. The Revit writer writes the geometry as mesh, in millimeters, without Revit parameters.
STL files store no units, so the 3D InterOp STL reader assumes millimeters. Agree on the unit with the application that wrote the file.
3D InterOp reads any STL version, as visualization data.
3D InterOp writes Revit 2026 families (.rfa).
Yes. 3D InterOp reads and writes both formats, so RFA to STL is supported too.
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Building software that needs to convert STL to RFA?
3D InterOp is an SDK that lets your application read STL and write Revit family alongside 30+ CAD and BIM formats.