Browser-based conversion
Use the converter without installing desktop software to move from 3DM to STL.
Free under 5 MB3DM → STLNo software installation
Convert 3DM
to STL online
Convert a 3DM (.3dm) CAD model into an STL (.stl) mesh for 3D printing, slicing and rapid prototyping. The converter tessellates the model's exact curves and surfaces into polygonal geometry that can be downloaded and inspected in your browser.
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 triangular mesh
Translate nurbs, solids, curves and meshes into the triangular surface mesh used by STL.
Ready for the next workflow
Open the result in Cura, PrusaSlicer and 3D printers 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 STL online
Move from Rhino 3DM to STL mesh 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 STL as the output
This page is preconfigured for 3DM-to-STL conversion, so you do not need to search through target formats.
Download and inspect the STL
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 STL?
3DM engineering geometry is tessellated into the polygonal surface structure used by STL. The visible shape is preserved, but parametric CAD intelligence is not.
Normally retained
- Overall 3D shape
- Vertices and surface geometry
- Tessellated faces
- Model orientation where supported
May not be retained
- Parametric feature history
- Editable sketches and constraints
- Assembly intelligence
- CAD metadata not supported by the mesh
Rhino 3DM3DM
STL meshSTLSTL is a mesh output. Keep the source 3DM file whenever editable engineering geometry may be needed later.
Format comparison
3DM versus STL
Choose the output according to what the next stage of your workflow needs.
| Feature | 3DM 3DM | STL STL |
|---|---|---|
| Main purpose | Rhino modelling, NURBS surfacing and mixed geometry | 3D printing, slicing and rapid prototyping |
| Geometry | NURBS, solids, curves and meshes | Triangular surface mesh |
| Textures and UV mapping | May contain texture references | Not supported in standard STL |
| Materials | Rhino materials may be included | Not supported in standard STL |
| Object groups | Layers and object groups may be included | Does not retain named object groups |
| Common workflow | Rhino and OpenNURBS-compatible tools | Cura, PrusaSlicer and 3D printers |
Choose STL when
Your next application or supplier specifically requires a STL file.
3D printing, slicing and rapid prototyping 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
STL 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
A source model created in centimetres may be interpreted as millimetres by another application. Confirm the expected size in the slicer.
- 02
Confirm the model is watertight
The surface should form a closed volume without open boundaries, gaps or holes that could create missing layers.
- 03
Inspect surface normals
Flipped or inconsistent normals can make faces appear missing or inside out. Repair them before slicing.
- 04
Find non-manifold geometry
Remove internal surfaces, overlapping faces and invalid edges that can stop the slicer from understanding the solid.
- 05
Check minimum wall thickness
A thin surface may be visible on screen but still be below the printable limit of the selected nozzle or process.
- 06
Preview every sliced layer
Look for unexpected gaps, floating islands, missing sections and incorrect scale before starting the print.
Common problems
3DM-to-STL conversion troubleshooting
Most conversion issues come from differences between file formats or problems already present in the source geometry.
The STL file has the wrong size
The source and destination tools may interpret units differently. Open the STL file and select the correct unit or scale.
Fix: Verify units and dimensionsTextures or materials disappeared
This can be expected when STL 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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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 STL online?
Upload your 3DM file (.3dm) to Marathon OS, choose STL as the output format, and download the converted file in seconds — no software installation required.
Why convert 3DM to STL?
Converting 3DM to STL prepares Rhino models for 3D printing, slicing, and mesh-based review.
What 3DM and STL file extensions are supported?
This converter accepts .3dm input files and outputs .stl. Upload up to 300 MB per file.
Is the 3DM to STL 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 STL directly in your browser. No plugins or desktop CAD tools required.
Can I convert large 3DM models to STL?
Yes — Marathon OS is optimized for large and complex CAD models. You can upload files up to 300 MB for 3DM to STL conversion.
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