Browser-based conversion
Use the converter without installing desktop software to move from STEP to 3DM.
Free under 5 MBSTEP → 3DMNo software installation
Convert STEP
to 3DM online
Convert a STEP (.step or .stp) CAD model into Rhino 3DM (.3dm) for Rhino, Grasshopper and OpenNURBS workflows. Compatible solids, shells, surfaces and curves are translated into Rhino-readable geometry without requiring desktop CAD software.
Encrypted uploads Files up to 300 MB Deleted after 7 days
Upload your STEP file
Choose one file to begin the conversion.
Drag and drop your 3D file here
or choose a file from your computer
Browse filesMaximum file size: 300 MB
Files under 5 MB convert and download free. For larger files, 1 credit = one download of any size — buy a pack.
Don't have a file? Try a sample:
Built for rhino / opennurbs
Translate b-rep solids and surfaces into the nurbs, solids, curves and meshes used by 3DM.
Ready for the next workflow
Open the result in Rhino and OpenNURBS-compatible tools for review, editing or production.
Private file handling
Converted models are not added to the public CAD library and are removed after processing.
Continue your CAD workflow
Explore Marathon
OS CAD resources
Preview a model before conversion, find an existing engineering file, open a 2D drawing, or get specialist help when a source mesh needs to be rebuilt.
Browse CAD modelsSearch ready-to-use engineering and 3D-printing files across the Marathon OS library.Browse 2D technical drawingsExplore PDF, SVG and DXF drawing resources for engineering review and documentation.Get CAD design supportWork with a vetted designer when the model needs repair, remodelling or a production-ready native file.
Simple conversion workflow
How to convert STEP to 3DM online
Move from STEP model to Rhino 3DM in three clear steps.
Upload your STEP file
Drag and drop the .step file into the converter or choose it from your device. Files up to 300 MB are supported.
Use 3DM as the output
This page is preconfigured for STEP-to-3DM conversion, so you do not need to search through target formats.
Download and inspect the 3DM
Download the result and open it in your preferred compatible application to confirm its geometry and scale.
Format behaviour
What changes when
STEP is converted to 3DM?
STEP and 3DM describe geometry differently. Conversion preserves compatible shape and topology while translating or omitting format-specific data.
Normally retained
- Overall model shape
- Compatible geometry
- Model orientation
- Supported topology and layers
May not be retained
- Format-specific metadata
- Unsupported materials or textures
- Application-specific features
- Data without a target-format equivalent
STEP modelSTEPRhino 3DM3DMKeep the original STEP file as the source of truth and inspect the converted 3DM file before downstream production use.
Format comparison
STEP versus 3DM
Choose the output according to what the next stage of your workflow needs.
| Feature | STEP STEP | 3DM 3DM |
|---|---|---|
| Main purpose | CAD exchange, manufacturing and editable engineering geometry | Rhino modelling, NURBS surfacing and mixed geometry |
| Geometry | B-rep solids and surfaces | NURBS, solids, curves and meshes |
| Textures and UV mapping | Not normally included | May contain texture references |
| Materials | Basic product data may be retained | Rhino materials may be included |
| Object groups | Assemblies and product structure may be retained | Layers and object groups may be included |
| Common workflow | SolidWorks, Fusion 360, Inventor and CAD/CAM tools | Rhino and OpenNURBS-compatible tools |
Choose 3DM when
Your next application or supplier specifically requires a 3DM file.
Rhino modelling, NURBS surfacing and mixed geometry is the next stage of the workflow.
The target geometry representation suits the downstream task.
Keep STEP when
Your project still depends on data unique to the source format.
You need to continue editing in SolidWorks, Fusion 360, Inventor and CAD/CAM tools.
The model is still being prepared rather than handed off.
Before continuing
Check the converted
3DM before the next step
Changing the file format does not automatically make a model production-ready. Review these checks in the application used for your next workflow.
Important: File formats may not include a standard unit definition. Always verify dimensions after conversion.
- 01
Verify dimensions and scale
Confirm that the converted 3DM file uses the expected size and unit interpretation.
- 02
Inspect the complete geometry
Check that all expected bodies, surfaces, curves or drawing entities are present.
- 03
Review surface orientation
Look for flipped faces, inconsistent normals or reversed boundaries after conversion.
- 04
Check topology and open edges
Inspect gaps, overlaps, invalid edges and disconnected geometry before downstream use.
- 05
Confirm layers and object structure
Verify that supported layers, groups and model organisation were translated as expected.
- 06
Open the file in its target application
Preview the 3DM result in the software used for the next workflow before production use.
Common problems
STEP-to-3DM conversion troubleshooting
Most conversion issues come from differences between file formats or problems already present in the source geometry.
The 3DM file has the wrong size
The source and destination tools may interpret units differently. Open the 3DM file and select the correct unit or scale.
Fix: Verify units and dimensionsTextures or materials disappeared
This can be expected when 3DM does not support the texture, UV or material information stored by STEP.
Fix: Keep the original STEP visual dataThe model has missing faces
The STEP source may contain open edges, invalid polygons, overlapping geometry or inverted normals that remain visible after conversion.
Fix: Inspect and repair the source geometryThe conversion fails on a large file
High polygon counts and complex geometry need more processing. Confirm the file is below 300 MB and opens correctly in a viewer.
Fix: Simplify unnecessary geometry detailSecure processing
Your 3D files remain yours
Product models can contain confidential engineering information. Privacy and file handling stay explicit beside the tool.
Encrypted upload
Files are transferred through a secure connection.
Automatic deletion
Uploaded and converted files are deleted after 7 days.
You retain ownership
Conversion does not transfer ownership of your model.
Not publicly listed
Your uploaded files are not added to the Marathon CAD library.
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Find a model before building from scratch
Browse engineering categories and recent 3D-printing models. Preview and validate every downloaded file before production use.
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Frequently asked questions
Everything to know before converting
Quick answers about formats, pricing, file limits, conversion quality and privacy.
How do I convert STEP to 3DM online?
Upload your STEP file (.step or .stp) to Marathon OS, choose 3DM as the output format, and download the converted file in seconds — no software installation required.
Why convert STEP to 3DM?
STEP is the standard CAD exchange format. Converting STEP to 3DM produces a Rhino-compatible mesh you can open in Rhinoceros without a STEP import plugin.
What STEP and 3DM file extensions are supported?
This converter accepts .step or .stp input files and outputs .3dm. Upload up to 300 MB per file.
Is the STEP to 3DM converter free?
Files under 5 MB are free to convert and download on Marathon OS. Larger files may require a small fee per conversion.
How is my data stored and secured?
Your files are encrypted during upload, processed securely in the cloud, and automatically deleted after 7 days.
Do I need any special software or training?
No — upload your STEP file and download 3DM directly in your browser. No plugins or desktop CAD tools required.
Can I convert large STEP models to 3DM?
Yes — Marathon OS is optimized for large and complex CAD models. You can upload files up to 300 MB for STEP to 3DM conversion.
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