STL to 3MF Converter
Put one or more STLs into a 3MF with real units, in your browser. No upload.
Binary or ASCII. They stay on this device.
STL holds only triangles. A 3MF also says what the units are and keeps separate parts apart.
- Several STLs become one 3MF, each its own object
- You say the units, because STL doesn’t
- Every part is checked, and the 3MF is read back before you get it
Working…
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This browser can’t show the 3D view (WebGL is off). The check and the download still work.
What changes when an STL becomes a 3MF
The shape doesn’t change. Every triangle goes across, except zero-area ones, which the 3MF format forbids. What you gain is units, separate named objects, and a file that’s usually a good deal smaller, because the 3MF is compressed and shares corners between faces.
STL can’t tell us the units, so you do. Most STLs for 3D printing are in millimetres. If yours came out 25 times too small in your slicer, it’s in inches.
Why some files are held back
The 3MF format says a mesh must be closed and face outward, and we hold to that. If a part has open edges or is inside out, the page says which part, and you can fix it in STL Repair or remove it. We read the finished 3MF back and compare its faces, volume and size with your STLs before the button turns on.
What was tested, and what wasn’t
We ran this page in a headless Chromium browser on our test files and 3 real STLs. Each 3MF was opened by lib3mf in strict mode, with no warnings, and by trimesh, and the volume matched the STL. Awkward files were refused or held back with a reason. We haven’t tried Safari or Firefox, or a real phone.
We haven’t opened these files in Bambu Studio, PrusaSlicer or OrcaSlicer, and nothing has been printed. Try one in your own slicer before relying on it. Read how we test.
FAQ
How do I convert STL to 3MF?
Drop your STL here, check the units, and press Download 3MF once the check passes. There’s nothing to install and no account.
Is my file uploaded?
No. The files are read and written by this browser tab. Every test run logs the requests made while a file is in use, and none of them holds a file, its name or any part of it. The page still sends a page-view count and one “tool finished” count, which name the tool and not your file.
Is 3MF better than STL?
It holds more: units, several objects, colours and settings. It’s smaller too. STL is simpler and works almost everywhere. This page adds units and separate objects. It can’t add colours, because the STL doesn’t have any.
Can I put several STLs into one 3MF?
Yes, up to 20. Each becomes its own named object. Side by side lays them out in a row with 5 mm between them. As in the files keeps the positions each STL already has, so parts that were designed together stay together.
Will the file be smaller?
In our tests the 3MF was about 17 to 29% of the STL’s size. The page shows both sizes for your file.
Why is the download off?
One of your files isn’t a closed solid, or the finished 3MF didn’t read back the same as your STLs. The list of parts says which one.
Does it work with Bambu Studio or PrusaSlicer?
The file follows the 3MF core specification, and a strict 3MF reader opens it with no warnings. We haven’t opened it in those slicers ourselves, as we don’t have them, so we can’t promise it.
How large a file can it take?
400 MB in total on a computer and 100 MB on a phone. These are this page’s own limits, not measured phone limits.
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