Browser-local converter
3MF to STL converter
Convert a 3MF package to STL without uploading it. 3MF is the one common maker format that records its own unit, so this conversion knows the real size of your model and can tell you what the STL will lose.
Drop your 3MF files here
STL, OBJ, PLY, GLB, glTF, 3MF and SVG. Nothing is uploaded: files are read and converted inside this tab. Checking what this device can handle...
Queue
No files yet. Drop models above, or use the file picker.
Output
Units
Size and placement
Repair and cleanup
These can change the shape, so they need a before-and-after review before export.
Inspection
Add a model to see its dimensions, mesh health and estimated volume.
What this 3MF to STL conversion does and does not do
- 3MF declares a unit; STL does not. The exported coordinates are unchanged, so the numbers still mean whatever the 3MF said they meant. The workspace shows you the real dimensions in millimetres before you export.
- The build section of a 3MF places objects with transforms, and components can nest. Those transforms are applied to the vertices, so the STL matches what you see, but the assembly structure itself is flattened into one shell.
- Base materials and display colours are read and shown, then dropped, because STL stores geometry only.
- 3MF extensions beyond the core specification, including production, slice and beam-lattice data, are not interpreted.
- A 3MF is a ZIP archive, so it is treated as untrusted input: entry counts, declared sizes, compression ratios and entry paths are all checked before anything is decompressed.
Troubleshooting
The 3MF will not open
The file must be a complete .3mf package, not the 3dmodel.model XML on its own. If the archive was re-zipped by hand the relationship part may be missing; re-export from your original tool.
Only part of the assembly came through
Only objects referenced by a build item are placed, which is what the specification requires. If your 3MF declares objects but no build items, the workspace includes them all and tells you it did so.
The size is wrong after import
Check what unit your slicer assumed. STL carries no unit, so if the 3MF was in centimetres or inches the raw numbers will be misread as millimetres. Convert units in the workspace before exporting.
Questions
Why convert 3MF to STL at all?
3MF is the better format on every technical measure, but a lot of older slicers, printer firmwares and print services still only accept STL. Converting is usually about compatibility, not quality.
Does this keep the colours?
No, and nothing can: STL has no colour channel. The workspace lists the materials it found so you know exactly what is being dropped. Convert to GLB if you need colour.
Is a 3MF from an unknown source safe to open here?
It is opened defensively. Zip bombs, path traversal, absurd entry counts and XML entity attacks are all refused before any expensive work happens, and nothing is ever written to your filesystem.