3MF to STL Converter
Drop a .3mf file and get its objects as STL: merged into one file, or one STL per object.
How to use
- Step 1Drop a .3mf from Bambu Studio, OrcaSlicer, PrusaSlicer, Cura or Windows 3D Builder. Project files with several objects on the plate, and the Bambu and Orca layout with meshes in separate parts, are all read.
- Step 2Leave "One STL file per object" off for a single STL with every object as placed on the plate, or turn it on to get one file per object named after the object. Press Convert.
- Step 3Load the STL into any slicer or CAD tool. Positions and millimetres are kept; colours, paint and print settings are not, because STL cannot hold them.
What a 3MF holds that STL cannot
3MF (3D Manufacturing Format) was published in 2015 by the 3MF Consortium as the replacement for STL in printing workflows. A .3mf file is a ZIP archive: the geometry sits in an XML part (3D/3dmodel.model) with an explicit unit (millimetres by default; microns, centimetres, inches, feet and metres are allowed), objects with names, a build section that places each object with a transform, and optional colours, materials and textures. Slicers use the same archive as their project format and add their own parts: Bambu Studio and OrcaSlicer keep print settings in Metadata/project_settings.config and object names in model_settings.config, PrusaSlicer in Slic3r_PE.config, and Cura in its own metadata.
STL is a bare list of triangles with none of that. Converting to it is a one-way trip: the file that comes out is smaller and universal, and everything the slicer knew about the print is gone.
| 3MF | STL | |
|---|---|---|
| Units | Declared in the file | None; read as millimetres |
| Several objects | Named, each with its placement | One merged mesh, or one file each |
| Colours and materials | Yes, including painted regions | None |
| Supports, modifiers, settings | Slicer project data | None |
| Compression | ZIP | Raw binary, 50 bytes per triangle |
How this page reads the file
The build items are walked in order. An item points at an object, which is either a mesh or a set of components pointing at other objects, each with its own transform; component transforms are composed with the item's, and a mirroring transform flips the triangle order so faces keep pointing outwards. Bambu Studio and OrcaSlicer use the 3MF Production extension, which stores each object's mesh in its own part under 3D/Objects and references it by path; those references are followed, which is why this page shows geometry where readers that only open the root part show nothing.
Merged output keeps every object where it sat on the plate, so objects do not land on top of each other. Per-object output also keeps the placement, so the files load back into a slicer in the same arrangement. Support objects marked as such in the file are skipped, since a slicer generates its own.
What is lost
- Colours and materials, including per-face painting from Bambu Studio and PrusaSlicer, which live in extension attributes only slicers read.
- Print settings, modifiers, paint-on supports and seams: they belong to the slicer project, not to the geometry.
- Object names in the merged file; with one file per object the name becomes part of the file name.
- Nothing about size: units are converted to millimetres, and the page shows the bounding box so you can check it.
Questions and answers
Why does the STL not have the colours I painted in Bambu Studio?
STL has no colour at all. Painting, multi-material assignments and colour groups are stored in 3MF extension attributes that only slicers understand. To keep them, stay with 3MF; convert to STL only for tools that need plain geometry.
The 3MF has three objects. What do I get?
By default one STL holding all three at their plate positions, with the object count in the stats. With "One STL file per object" you get three downloads, each named after its object, or object-1, object-2 when the file has no names.
Why do other converters show an empty model for my Bambu Studio or OrcaSlicer file?
Those slicers write the 3MF Production extension: the root part contains only references, and the meshes sit in 3D/Objects/*.model parts. A reader that opens only 3D/3dmodel.model finds no triangles. This page follows the references, so the objects appear.
Is the STL at the right size?
Yes. 3MF declares its unit and the page converts to millimetres, the unit every slicer assumes for STL. A 3MF written in inches comes out 25.4 times larger in number and identical in real size. Check the size shown next to the download.
Can I go back to 3MF later?
Every current slicer saves its project as 3MF: load the STL, arrange and paint it, then save the project. Colours and settings you add there are stored in the new file; the ones from the original 3MF are not recovered.