Starter
3credits
$7.99
$2.66 each
3 downloads of any size. Good for a one-off project.
First 2 conversions free3MF → STLNo software installation
Convert 3MF
to STL online
Convert a 3MF (.3mf) print file into STL online. Upload your file in the browser and download the converted result without installing desktop CAD software.
Encrypted uploads Files up to 300 MB Automatically deleted within 7 days
Upload your 3MF file
Choose one file to begin the conversion.
Drag and drop your file here
or choose a file from your computer
Browse filesMaximum file size: 300 MB
First 2 conversions free — any size up to 300 MB. Then $2.99 or 1 credit per file, charged at download.
Pricing
Pay as you go, cheaper by the pack
Your first 2 CAD file conversions are free, any size up to 300 MB, including the download. From conversion 3 on, each file costs 1 credit or a one-time payment, charged only when you click Download. 1 credit downloads any file up to 300 MB, and credits never expire.
Save 11%
Pro
5credits
$12.99
$2.60 each
5 downloads of any size. The everyday choice.
Team
10credits
$19.99
$2.00 each
10 downloads of any size. Best balance of price and volume.
Studio
15credits
$26.99
$1.80 each
15 downloads of any size. Lowest price per file.
Browser-based conversion
Use the converter without installing desktop software to move from 3MF to STL.
Built for triangular mesh
Translate triangle meshes with declared units 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 3MF to STL online
Move from 3MF print file to STL mesh in three clear steps.
Upload your 3MF file
Drag and drop the .3mf 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 3MF-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 3MF is converted to STL?
3MF and STL 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
3MF print file3MFSTL meshSTLKeep the original 3MF file as the source of truth and inspect the converted STL file before downstream production use.
Format comparison
3MF versus STL
Choose the output according to what the next stage of your workflow needs.
| Feature | 3MF 3MF | STL STL |
|---|---|---|
| Main purpose | 3D printing, slicing and multi-part print jobs | 3D printing, slicing and rapid prototyping |
| Geometry | Triangle meshes with declared units | Triangular surface mesh |
| Textures and UV mapping | Colours supported; textures through extensions | Not supported in standard STL |
| Materials | Base materials and colours can be stored | Not supported in standard STL |
| Object groups | Multiple named objects in one file | Does not retain named object groups |
| Common workflow | PrusaSlicer, Bambu Studio, OrcaSlicer and Cura | 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 3MF when
Your project still depends on data unique to the source format.
You need to continue editing in PrusaSlicer, Bambu Studio, OrcaSlicer and Cura.
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
3MF-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 3MF.
Fix: Keep the original 3MF visual dataThe model has missing faces
The 3MF 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.
Popular conversions
CAD converter types
Move into another common engineering workflow using one of Marathon OS's most-used conversion paths.
STEPSTL
STEP to STL
Convert STEP to STL for 3D printing and slicing.
STEP3DM
STEP to 3DM
Convert STEP to Rhino 3DM for Rhino workflows.
IGESSTEP
IGES to STEP
Convert IGES to STEP for manufacturing handoff.
OBJSTL
OBJ to STL
Convert OBJ to STL for mesh workflows and 3D printing.
STLSTEP
STL to STEP
Convert STL to STEP for CAD compatibility and import.
3DMSTEP
3DM to STEP
Convert Rhino 3DM to STEP for CAD/CAM exchange.
BREPSTL
BREP to STL
Convert BREP to STL for mesh export and 3D printing.
STEP3MF
STEP to 3MF
Convert STEP to 3MF for 3D printing with parts and colours kept.
DWGDXF
DWG to DXF
Convert DWG to DXF for 2D CAD exchange.
Marathon OS Design Hub
Find a model before building from scratch
Browse engineering categories and recent 3D-printing models. Preview and validate every downloaded file before production use.
3d-printing
3D Print-in-Place Fidget Rings with Stand for Prototyping
STEP engineering modelFree
3d-printingFdm 7 | 3D CAD Engineering Model
STEP engineering modelFree
3d-printingRe Entrant Honeycomd Design 1 | 3D CAD Engineering Model
STEP engineering modelFree
3d-printing3D Cnc Printer 1 | 3D CAD Engineering Model
STEP engineering modelFree
3d-printingDragon Letter C | 3D Engineering Design File
STEP engineering modelFree
3d-printingInnovative Rolling Habitat Transport System for Lunar Surface
STEP engineering modelFree
Frequently asked questions
Everything to know before converting
Quick answers about formats, pricing, file limits, conversion quality and privacy.
How do I convert 3MF to STL online?
Upload your 3MF file (.3mf) to Marathon OS, choose STL as the output format, and download the converted file in seconds — no software installation required.
Why convert 3MF to STL?
Converting 3MF to STL is useful when a print service or older slicer only accepts STL. Colours and object names are not kept, because STL cannot store them.
What 3MF and STL file extensions are supported?
This converter accepts .3mf input files and outputs .stl. Upload up to 300 MB per file.
Is the 3MF to STL converter free?
Your first 2 CAD file conversions on Marathon OS are free, any size up to 300 MB. After that, each converted file needs a small fee or 1 credit, paid only when you download it.
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 3MF file and download STL directly in your browser. No plugins or desktop CAD tools required.
Can I convert large 3MF models to STL?
Yes — Marathon OS is optimized for large and complex CAD models. You can upload files up to 300 MB for 3MF to STL conversion.