What Does a 3MF to STL Converter Do?
3MF and STL are both file formats for 3D models. 3MF is the newer one: it is a small zip compressed package that can hold several objects, their positions on the build plate, colours, materials and slicer settings. STL is older and much simpler - it only stores the surface of a model as a list of triangles.
Many tools still only accept STL, such as older slicers, some online print services, CAD importers and 3D model sites. This converter reads the 3D shapes inside your 3MF file and writes them out as a standard STL file you can use anywhere.
What Is Kept and What Is Lost
Because STL can only describe shape, some information in a 3MF file has nowhere to go:
| Information in the 3MF | In the STL? |
|---|---|
| 3D shape (triangle mesh) | Kept - every triangle, at full STL precision |
| Multiple objects | Kept - all merged into one STL, each in its own position |
| Position, rotation, scale | Kept - applied to the shape |
| Units | Kept as size - output in millimetres (see below) |
| Colours and painted areas | Lost - STL has no colour |
| Materials and textures | Lost |
| Print and slicer settings | Lost |
| Separate object names | Lost - STL holds one combined shape |
If you need colours or several separate objects, keep using the 3MF file in your slicer, and use the STL only where STL is required.
Units: Why the STL Is in Millimetres
STL files do not record which unit they use. Almost every slicer and 3D printing service treats STL numbers as millimetres. A 3MF file, on the other hand, states its unit - usually millimetres, but sometimes inches, centimetres or metres.
So that your model opens at the correct real-world size, the converter scales it to mm when the 3MF uses a different unit. If you need the original numbers unchanged, you can choose to keep the original units after converting. Files that are already in millimetres are never scaled.
Private by Design
The whole conversion happens inside your web browser, on your own phone or computer. Your 3MF file is not uploaded to Compressly or to any other server, and the STL file is created on your device.
Works With Files From Popular Slicers
The converter follows the official 3MF specification, so it handles project files from Bambu Studio, OrcaSlicer, PrusaSlicer, Cura, Microsoft 3D Builder and other apps - including Bambu and Orca files that keep each object in a separate part of the package, which some converters turn into an empty STL.