Browser-based conversion
Use the converter without installing desktop software to move from 3DM to STEP.
Free under 5 MB3DM → STEPNo software installation
Convert 3DM
to STEP online
Convert a 3DM (.3dm) CAD model into STEP (.step or .stp) for mechanical CAD exchange and downstream engineering workflows. The converter translates compatible curves, surfaces, solids and topology while preserving engineering geometry wherever the destination format supports it.
Encrypted uploads Files up to 300 MB Deleted after 7 days
Upload your 3DM 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 parametric cad
Translate nurbs, solids, curves and meshes into the b-rep solids and surfaces used by STEP.
Ready for the next workflow
Open the result in SolidWorks, Fusion 360, Inventor and CAD/CAM 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 3DM to STEP online
Move from Rhino 3DM to STEP model in three clear steps.
Upload your 3DM file
Drag and drop the .3dm file into the converter or choose it from your device. Files up to 300 MB are supported.
Use STEP as the output
This page is preconfigured for 3DM-to-STEP conversion, so you do not need to search through target formats.
Download and inspect the STEP
Download the result and open it in your preferred compatible application to confirm its geometry and scale.
Format behaviour
What changes when
3DM is converted to STEP?
3DM and STEP 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
Rhino 3DM3DMSTEP modelSTEPKeep the original 3DM file as the source of truth and inspect the converted STEP file before downstream production use.
Format comparison
3DM versus STEP
Choose the output according to what the next stage of your workflow needs.
| Feature | 3DM 3DM | STEP STEP |
|---|---|---|
| Main purpose | Rhino modelling, NURBS surfacing and mixed geometry | CAD exchange, manufacturing and editable engineering geometry |
| Geometry | NURBS, solids, curves and meshes | B-rep solids and surfaces |
| Textures and UV mapping | May contain texture references | Not normally included |
| Materials | Rhino materials may be included | Basic product data may be retained |
| Object groups | Layers and object groups may be included | Assemblies and product structure may be retained |
| Common workflow | Rhino and OpenNURBS-compatible tools | SolidWorks, Fusion 360, Inventor and CAD/CAM tools |
Choose STEP when
Your next application or supplier specifically requires a STEP file.
CAD exchange, manufacturing and editable engineering geometry is the next stage of the workflow.
The target geometry representation suits the downstream task.
Keep 3DM when
Your project still depends on data unique to the source format.
You need to continue editing in Rhino and OpenNURBS-compatible tools.
The model is still being prepared rather than handed off.
Before continuing
Check the converted
STEP 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 STEP 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 STEP result in the software used for the next workflow before production use.
Common problems
3DM-to-STEP conversion troubleshooting
Most conversion issues come from differences between file formats or problems already present in the source geometry.
The STEP file has the wrong size
The source and destination tools may interpret units differently. Open the STEP file and select the correct unit or scale.
Fix: Verify units and dimensionsTextures or materials disappeared
This can be expected when STEP does not support the texture, UV or material information stored by 3DM.
Fix: Keep the original 3DM visual dataThe model has missing faces
The 3DM 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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CAD converter types
Move into another common engineering workflow using one of Marathon OS's most-used conversion paths.
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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 3DM to STEP online?
Upload your 3DM file (.3dm) to Marathon OS, choose STEP as the output format, and download the converted file in seconds — no software installation required.
Why convert 3DM to STEP?
Converting 3DM to STEP helps move Rhino models into CAD/CAM and manufacturing workflows that expect STEP exchange files.
What 3DM and STEP file extensions are supported?
This converter accepts .3dm input files and outputs .step or .stp. Upload up to 300 MB per file.
Is the 3DM to STEP 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 3DM file and download STEP directly in your browser. No plugins or desktop CAD tools required.
Can I convert large 3DM models to STEP?
Yes — Marathon OS is optimized for large and complex CAD models. You can upload files up to 300 MB for 3DM to STEP conversion.
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