Turn STL files into 3MF for your slicer. The 3MF records the model’s unit and is usually much smaller than the STL.
Drop STL files hereRelease to convert
or
STL (binary or ASCII), a folder or a ZIP · up to 200 files
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Drop more STL files hereRelease to convert
STL files or a ZIP · up to 200 files
Click a file to preview it.
Preview
Settings
STL stores no units. Pick what the model was made in; the 3MF records it.
Merges corners that almost touch, closing hairline gaps so slicers see one solid.
How it works
Choose your STL files
Binary or ASCII; drop files, a folder or a ZIP. They are read by your browser and never sent anywhere.
Pick the unit
Millimetres unless the model was made in something else. The preview reads the finished 3MF back.
Download the 3MF
One file at a time, or all of them as a single ZIP.
Settings explained
STL units
STL files hold plain numbers. A 3MF records the unit, so pick what the STL was made in: the numbers are kept as they are and the unit is written into the 3MF. Slicers then open the part at the right size, even when they are set to inches.
Almost every STL is in millimetres, which is the default.
Weld duplicate vertices
3MF stores each corner once and lets the triangles share it. Corners that are exactly the same are always merged, which keeps the mesh closed and the file small.
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 merged too. That closes hairline gaps left by rounding in the STL, and triangles that collapse to a line are removed.
STL vs 3MF
STL is a plain list of triangles, each with its own three corners, and says nothing about units. 3MF stores each corner once, records the unit, and packs the model into a compressed ZIP, which is why the same part is usually much smaller.
3MF can also hold colours, materials and several objects placed on a plate. An STL brings none of that, so the converted 3MF holds one object; add the rest in your slicer.
| Property | STL | 3MF |
|---|---|---|
| Full name | Stereolithography (also read as Standard Triangle Language) | 3D Manufacturing Format |
| Extension | .stl | .3mf |
| MIME type | model/stl | model/3mf |
| Encoding | Binary or text (ASCII) | ZIP archive with XML |
| Surface | Triangles only | Triangles |
| Shared vertices | No, every triangle stores its own corners | Yes |
| Colours and materials | No, not in the standard | Yes, colours and materials in the file |
| Units | Not stored | Yes: micron, mm, cm, inch, foot or metre |
| Several objects | No, one list of triangles | Yes, with their place on the build plate |
| Opened by | Every slicer and CAD program | Slicers (PrusaSlicer, Bambu Studio, OrcaSlicer, Cura) and Windows 3D Builder |
FAQ
Which unit should I choose?
The one the model was made in. STL stores plain numbers, and almost every STL from CAD or a model site is in millimetres, the default. The numbers are kept as they are and the unit is written into the 3MF, so slicers open the part at the right size.
Is the 3MF smaller than the STL?
Usually much smaller. A 3MF stores each corner once and is compressed as a ZIP, while a binary STL stores every corner three times. Our 1-million-triangle test cube shrinks from 48 MB to 6.8 MB; its regular coordinates compress unusually well, so expect less on scanned or organic models. A very small STL can come out larger, because the ZIP package has a fixed overhead: our 684-byte test cube becomes a 1.1 KB 3MF.
Can I add colours or combine several parts into one 3MF?
Not here. Each STL becomes its own 3MF with one object and no colours, since the STL has none. Paint the model or arrange several parts on one plate in your slicer, and save that as a project.
Why convert to 3MF at all?
A 3MF records its unit, so a part made in inches cannot arrive 25.4 times too small, and its smaller size is easier to share. PrusaSlicer, Bambu Studio, OrcaSlicer and Cura all open 3MF directly.
Why does Bambu Studio say “invalid config, load geometry data only”?
Bambu Studio shows it for any 3MF without Bambu project settings (printer, filament and process), not only for files from here. The geometry is correct: with the default settings, size, volume and triangle count are preserved exactly. Weld duplicate vertices can lower the triangle count slightly, since corners that are nearly the same are merged. Pick your printer and filament as usual and print.
What does Weld duplicate vertices change?
A 3MF always stores corners shared by triangles once, so exact duplicates are merged either way. With Weld on, corners that are only nearly the same are merged too, which closes hairline gaps left by some exporters.
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.