Turn 3MF files and slicer projects into STL. Every object stays where it sits on the plate, and the 3MF’s unit is converted to millimetres.
Drop 3MF files hereRelease to convert
or
3MF files, a folder or a ZIP · up to 200 files
No file at hand?
Drop more 3MF files hereRelease to convert
3MF files or a ZIP · up to 200 files
Click a file to preview it.
Preview
Settings
Binary is smaller and opened by every slicer. ASCII is human-readable.
The 3MF’s own unit is converted to this. Slicers expect millimetres.
Merges corners that almost touch, closing hairline gaps so slicers see one solid.
How it works
Choose your 3MF files
Drop files, a folder or a ZIP. They are read by your browser and never sent anywhere.
Check the preview
See the size in mm, the triangle count and whether the mesh is watertight, with every part in place.
Download the STL
One file at a time, or all of them as a single ZIP.
Settings explained
STL encoding
Binary STL stores each triangle in 50 bytes after an 84-byte header, and every slicer and CAD program reads it. ASCII STL writes the same triangles as text, which makes the file about four times larger (3.8 times for a 1-million-triangle test model).
Choose ASCII only if you want to read, search or compare the file as text. The shape is the same either way.
STL units
A 3MF file says which unit its numbers are in: micron, millimetre, centimetre, inch, foot or metre. STL cannot say, and slicers read STL as millimetres, so the converter turns the 3MF’s unit into millimetres by default. A part saved in inches gets every number multiplied by 25.4, and the file list says so.
Choose another unit only if the STL goes to a program that expects it.
Weld duplicate vertices
STL stores every triangle with its own three corners. After an export, corners that should be the same point sometimes differ in the last decimal, which leaves hairline gaps that slicers report as holes or non-manifold edges.
With Weld on, corners closer than 1/100 000 of the model’s bounding-box diagonal (about 0.002 mm on a 100 mm cube) are moved onto one point, and triangles that collapse to a line are removed. With Weld off, every triangle is written exactly as it was read.
3MF vs STL
3MF is a ZIP package. It records the unit, colours and materials, and where each object sits on the build plate, and slicers keep their print settings in it. STL is a plain list of triangles with none of that.
Converting to STL keeps the triangles of every object in the build, in place and in millimetres, and drops the rest. Convert to STL when a program only reads STL, or to share the bare geometry of a project.
| Property | 3MF | STL |
|---|---|---|
| Full name | 3D Manufacturing Format | Stereolithography (also read as Standard Triangle Language) |
| Extension | .3mf | .stl |
| MIME type | model/3mf | model/stl |
| Encoding | ZIP archive with XML | Binary or text (ASCII) |
| Surface | Triangles | Triangles only |
| Shared vertices | Yes | No, every triangle stores its own corners |
| Colours and materials | Yes, colours and materials in the file | No, not in the standard |
| Units | Yes: micron, mm, cm, inch, foot or metre | Not stored |
| Several objects | Yes, with their place on the build plate | No, one list of triangles |
| Opened by | Slicers (PrusaSlicer, Bambu Studio, OrcaSlicer, Cura) and Windows 3D Builder | Every slicer and CAD program |
FAQ
Do I need to convert at all?
Not for printing. Bambu Studio, PrusaSlicer and OrcaSlicer open 3MF directly. Convert if the file is going to Tinkercad, Blender, an older slicer or someone who asks for STL.
Can I convert a Bambu Studio or PrusaSlicer project?
Yes. Slicer projects keep each part in its own model file inside the 3MF; the converter follows those references and places every part where it sits on the plate. Print settings, painted supports and plate thumbnails are not geometry, so they are not part of the STL.
Are the objects on the plate kept apart?
No. STL has no way to keep objects apart, so all of them are merged into one STL at their positions on the plate, and the file list says how many were merged. PrusaSlicer, Bambu Studio and OrcaSlicer can split it into separate parts again with Split to objects.
What happens to the units?
A 3MF says which unit it uses; STL cannot. The converter turns the 3MF’s unit into millimetres, which slicers expect, so a part saved in inches gets every number multiplied by 25.4. The file list notes every conversion like that. Choose another unit under STL units if the STL is for a program that expects it.
What happens to colours and materials?
STL cannot store them, so they are dropped and the file list says so. The shape is not affected.
Why does a 3MF file not convert?
The converter reads the triangle meshes of the 3MF core specification, including parts stored in separate model files. A file whose ZIP archive is damaged or cut off, or that holds no triangle mesh at all, cannot be converted, and the file list says which of these it is.
How can I check that nothing is uploaded?
Open your browser’s developer tools, go to the Network tab and convert a file. You will see no request carrying your file. Once the page has loaded, converting works without an internet connection.