Convert STP to RFA in your application
3D InterOp is a CAD interoperability SDK that lets your software read STP 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 STEP · Writes Revit family
- Exact geometry → triangle mesh
- C++ / C# APIs
STP to RFA at a glance
STEP stores exact geometry; Revit family stores triangles. The translation is a tessellation, and the settings you choose decide how close the mesh stays to the original.
| STEP (source) | Revit family (target) | |
|---|---|---|
| Full name | Standard for the Exchange of Product model data | Revit family |
| Standard / owner | ISO 10303 — AP203, AP214, AP242 | Autodesk |
| File extensions | .stp, .step | .rfa |
| Geometry | Exact B-Rep | B-Rep and mesh (read); mesh (written by 3D InterOp) |
| Assemblies / structure | Yes | Nested families; assembly structure written by 3D InterOp |
| 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 Revit family.
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Preserved
Product structureThe STP product structure is written to RFA.
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Improved
Healed geometry3D InterOp repairs and heals STEP data during translation.
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Changes
Geometry written as meshThe Revit writer writes mesh only: exact B-Rep from STP isn’t exported to the family.
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Not carried
PMIThe Revit writer writes no PMI, so the PMI read from STP isn’t written. Keep STEP AP242 as an output when PMI matters.
Why software vendors add STP 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 STP input: AP203, AP214 and AP242.
- 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 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).
The Revit writer writes no PMI, so the PMI read from STP isn’t written. When PMI matters, offer STEP AP242 as an output.
Yes. 3D InterOp reads the STP product structure and writes it to RFA.
No. The Revit writer writes the geometry as mesh, in millimeters, without Revit parameters.
3D InterOp reads AP203, AP214 and AP242.
3D InterOp writes Revit 2026 families (.rfa).
Yes. 3D InterOp reads and writes both formats, so RFA to STP is supported too.
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Building software that needs to convert STP to RFA?
3D InterOp is an SDK that lets your application read STEP and write Revit family alongside 30+ CAD and BIM formats.