Convert STL to 3MF
Free · no signup · no watermark · runs in your browser · batch up to 20 files, download as ZIP
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3MF fixes the oldest problems of STL: it records the unit, so a part cannot arrive a thousand times too small, it welds the mesh so slicers see a closed solid, and it holds several objects with colours in one file. This converter wraps your STL files into a valid 3MF package in your browser, with the unit you choose (millimetres by default).
This conversion runs entirely in your browser. The file is never uploaded, which makes it instant, private and usable on work files you would not want to send to a stranger's server.
It also works as a bulk STL to 3MF converter: drop up to 20 STL files at once, they are converted one after another in your browser, and you can download each file on its own or all of them together in a single ZIP. A file that fails is listed with the reason and does not stop the rest of the batch.
How to convert STL to 3MF
- Drop your STL files onto the box above, or click it to choose from your computer. Up to 20 at once.
- Check the 3D preview and model info. If the model is the wrong size or lying on its back, open the options to set the source units or rotate Z-up to Y-up, then press Convert.
- Download each converted file from the list, or press "Download all (.zip)" to get the whole batch in one ZIP file.
What changes when you convert STL to 3MF
3MF keeps each object as a welded triangle mesh with one display colour and a declared unit. Textures and UVs are dropped; that is normal for printing.
STL has no units, so choose what its numbers mean (the default is millimetres). 3MF records the unit in the file.
STL and 3MF compared
| STL | 3MF | |
|---|---|---|
| Full name | Stereolithography | 3D Manufacturing Format |
| Extension | .stl | .3mf |
| MIME type | model/stl | model/3mf |
STL: The 3D printing workhorse: a list of triangles and nothing else. No colour, no materials, no UVs and no units (millimetres by convention), which is why every slicer and CAD tool can read it.
3MF: The modern 3D printing format: a zipped XML package with declared units, multiple objects and colours. Read by PrusaSlicer, Cura, Bambu Studio, OrcaSlicer and Windows 3D Builder.
Frequently asked questions
How do I convert STL to 3MF?
Drop your .stl file onto the box on this page and the .3mf file is ready to download in a second or two. There is no signup, no email, no watermark and no file limit beyond what your browser can hold in memory.
Is this STL to 3MF converter free?
Yes, completely, with no account, no trial and no watermark on the output. There is nothing to buy on this page: choose a file, convert it and download the result.
Are my files uploaded anywhere?
No. This conversion runs entirely in your browser using JavaScript, so the file never leaves your computer. You can disconnect from the network after the page loads and it will still work.
Will converting to 3MF reduce the quality?
3MF keeps each object as a welded triangle mesh with one display colour and a declared unit. Textures and UVs are dropped; that is normal for printing.
Can I convert multiple STL files to 3MF at once?
Yes, up to 20 files in one go. Drop or select them all together and they are converted one after another. Each file appears in the results list with its own download button, and "Download all (.zip)" saves the whole batch as a single ZIP. If one file cannot be converted, it is listed with the reason and the others still finish. For more than 20, run a second batch.
Found a problem, or something that could be better? We read every message and we fix things quickly.
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